Illumination device control systems and methods

ABSTRACT

In various embodiments, a control system for an electronic circuit iteratively applies voltage to and senses current from a load to regulate operation of the load.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/740,909, filed Jun. 16, 2015, which is a continuation-in-part of U.S.patent application Ser. No. 14/538,392, filed Nov. 11, 2014, which is acontinuation of U.S. patent application Ser. No. 14/271,938, filed May7, 2014, which is a continuation of U.S. patent application Ser. No.13/965,392, filed Aug. 13, 2013, which claims the benefit of andpriority to U.S. Provisional Patent Application No. 61/813,027, filedApr. 17, 2013, the entire disclosure of each of which is incorporatedherein by reference.

TECHNICAL FIELD

In various embodiments, the present invention relates generally tolight-emitting systems and methods, and more specifically to suchsystems and methods that provide control over various lightingparameters in systems featuring strings of light-emitting elements.

BACKGROUND

Solid-state lighting is an attractive alternative to incandescent andfluorescent lighting systems because of its relatively higherefficiency, robustness and long life. However, many solid-state lightingsystems utilize light-emitting diodes (LEDs) that require differentdrive circuitry than incandescent and fluorescent light emitters. LEDsare typically operated in current-control mode, in which the currentthrough the LED is controllably set to particular values to achievedesired optical characteristics, such as brightness levels.

Manufacturing variations in electronic components may result in adistribution of electrical and optical parameters. For example, in thecase of LEDs, there is generally a distribution in parameters such asforward voltage, light output power and wavelength. For LED-basedlighting systems, particularly where such systems include arrays ofLEDs, such variations result in the need for a system that canaccommodate possible variations not only in the manufacturingdistribution, but also that may arise from other sources, such asambient or operational temperature variations, aging, or the like. Thisapplies not only to light-emitting elements (LEEs), such as LEDs, but toall other active and passive components that may be in the system, e.g.,to control the current to the LEDs or to power the entire system.

For example, consider the system shown in FIG. 1, which features one ormore strings 160 of series-connected LEEs 110 and a current-controlelement (CCE) 120. The combination of the LEEs and the CCEs may becalled a light-emitting array. A light-emitting array may include orconsist essentially of one or more than one light-emitting string 160.The string voltage is the voltage of the sum of the forward voltages ofthe individual LEEs at the desired operating current added to thevoltage dropped across CCE 120. In one example, for GaN-based blue LEDs,the forward voltage, for a fixed current, may be in the range of about2.6 V to about 3.1 V, depending on variations in the LED fabricationprocess. Thus, depending on the distribution of forward voltagecharacteristics, the voltage across the 10 LEDs in FIG. 1 may range fromabout 26 V to about 31 V. For a light-emitting array with multiplestrings in parallel, as shown in FIG. 1, a string with a relatively lowstring voltage will generally result in a relatively higher voltagedropped over CCE 120, whereas a string with a relatively higher stringvoltage will generally have a relatively lower voltage dropped over CCE120. In the design of such systems the voltage of power supply 130 mustbe large enough to accommodate the highest possible string voltagewithin the manufacturing and operational distribution of thelight-emitting array as well as the voltage supply.

Consider a relatively common case where the forward voltage of each LEEis nominally about 2.9 V and the nominal voltage drop across CCE 120 isabout 2 V. For a string of 10 LEEs, the string voltage is then about 31V. This sets the nominal value of voltage to be supplied to thelight-emitting array at about 31 V.

Now consider the scenario where the string voltage is on the high end ofthe range, for example where the LEE forward voltage is about 3.1 V andthe voltage drop across the 10 LEEs is about 31 V. In some embodiments,CCE 120 may require at least about 2 V to operate, so the light-emittingarray requires a supplied voltage of 33 V, 2 V higher than the nominalamount. Next, consider the scenario where the string voltage is on thelow end of the range, for example where the LEE forward voltage is about2.7 V. The voltage drop across the 10 LEEs is then about 27 V.

In this situation, the voltage supply needs to be about 33 V toaccommodate the high end of the LEE forward voltage distribution.However, in the nominal case, the voltage dropped across CCE 120 is 4 Vand in the minimum forward voltage case it is 6 V. Thus, the powerdissipated in CCE 120 in the nominal case is twice that of the maximumforward voltage case, and the power dissipated in CCE 120 in the minimumforward voltage case is three times that of the maximum forward voltagecase. Even without accounting for other variations, such as in thevoltage supply, CCE 120, or operational variations, it is clear thatsuch a design may be optimized for efficiency in a narrow set ofparameter ranges, but as a result of manufacturing and operationalvariations, may operate at significantly lower efficiencies. Further,the additional power dissipated in CE 120 results in additional heat,which may be difficult to remove and may also lead to thermaldegradation and a reduction in lifetime and/or reliability.

One approach to mitigating this problem is reduce the manufacturingand/or operational variations that might be encountered, for example bysorting and binning LEEs, using higher precision components in thevoltage supply and CCE, controlling the ambient temperature range, orthe like. However, these approaches are undesirable because they aretime consuming and expensive.

Accordingly there is a need for solutions that provide improved drivecapability for LEE systems, in particular providing improved control ofcurrent through the LEEs as well as high efficiency.

SUMMARY

In accordance with certain embodiments, the signature of therelationship between load current and applied voltage is dynamicallyevaluated and used to set a desired voltage level that matches the loadto achieve a desired operational result, e.g., optimizing a given systemfor efficiency. Different voltages are applied to the load and thedifference in resulting currents is utilized to adjust the subsequentapplied voltage. This iterative procedure is generally performed duringthe entire operation of the load, rather than merely during a “start-up”period soon after power is initially applied. In this manner, variationsin the electrical characteristics of the load due to aging and/orenvironmental (e.g., temperature) changes are addressed via changes inthe applied voltage, thereby regulating operation of the load andoptimizing its efficiency. Furthermore, the control system may beutilized with any of a variety of different loads having differentelectrical characteristics (e.g., current-voltage characteristics) whileautomatically optimizing efficiency thereof.

Additional details of lighting systems in accordance with embodiments ofthe present invention appear within U.S. patent application Ser. No.13/970,027, filed Aug. 19, 2013 (the '027 application), U.S. patentapplication Ser. No. 13/799,807, filed Mar. 13, 2013 (the '807application), and U.S. patent application Ser. No. 13/748,864, filedJan. 24, 2013 (the '864 application), the entire disclosure of each ofwhich is incorporated by reference herein.

As utilized herein, the term “light-emitting element” (LEE) refers toany device that emits electromagnetic radiation within a wavelengthregime of interest, for example, visible, infrared or ultravioletregime, when activated, by applying a potential difference across thedevice or passing a current through the device. Examples of LEEs includesolid-state, organic, polymer, phosphor-coated or high-flux LEDs,microLEDs (described below), laser diodes or other similar devices aswould be readily understood. The emitted radiation of a LEE may bevisible, such as red, blue or green, or invisible, such as infrared orultraviolet. A LEE may produce radiation of a spread of wavelengths. ALEE may feature a phosphorescent or fluorescent material for convertinga portion of its emissions from one set of wavelengths to another. A LEEmay include multiple LEEs, each emitting essentially the same ordifferent wavelengths. In some embodiments, a LEE is an LED that mayfeature a reflector over all or a portion of its surface upon whichelectrical contacts are positioned. The reflector may also be formedover all or a portion of the contacts themselves. In some embodiments,the contacts are themselves reflective.

An LEE may be of any size. In some embodiments, an LEE has one lateraldimension less than 500 μm, while in other embodiments an LEE has onelateral dimension greater than 500 μm. Exemplary sizes of a relativelysmall LEE may include about 175 μm by about 250 μm, about 250 μm byabout 400 μm, about 250 μm by about 300 μm, or about 225 μm by about 175μm. Exemplary sizes of a relatively large LEE may include about 1000 μmby about 1000 μm, about 500 μm by about 500 μm, about 250 μm by about600 μm, or about 1500 μm by about 1500 μm. In some embodiments, an LEEincludes or consists essentially of a small LED die, also referred to asa “microLED.” A microLED generally has one lateral dimension less thanabout 300 μm. In some embodiments, the LEE has one lateral dimensionless than about 200 μm or even less than about 100 μm. For example, amicroLED may have a size of about 225 μm by about 175 μm or about 150 μmby about 100 μm or about 150 μm by about 50 μm. In some embodiments, thesurface area of the top surface of a microLED is less than 50,000 μm² orless than 10,000 μm². The size of the LEE is not a limitation of thepresent invention, and in other embodiments the LEE may be relativelylarger, e.g., the LEE may have one lateral dimension on the order of atleast about 1000 μm or at least about 3000 μm. In some embodiments theLEE may emit white light or substantially white light.

In some embodiments, various elements such as substrates or lightsheetsare “flexible” in the sense of being pliant in response to a force andresilient, i.e., tending to elastically resume an original configurationupon removal of the force. Such elements may have a radius of curvatureof about 1 m or less, or about 0.5 m or less, or even about 0.1 m orless. In some embodiments, flexible elements have a Young's Modulus lessthan about 100 N/m², less than about 50 N/m², or even less than about 10N/m². In some embodiments, flexible elements have a Shore A hardnessvalue less than about 100; a Shore D hardness less than about 100;and/or a Rockwell hardness less than about 150.

In an aspect, embodiments of the invention feature a method forcontrolling a circuit via application of first and second voltages. Thecircuit incorporates a load having electrical characteristics, which mayinclude or consist essentially of a non-linear current-voltagerelationship. In a step (A), the first voltage is applied to the load.In a step (B), a first current resulting from the first voltage appliedto the load is measured. In a step (C), the second voltage is applied tothe load. In a step (D), a second current resulting from the secondvoltage applied to the load is measured. A current difference betweenthe second current and the first current has a magnitude and a polarity.In a step (E), the first voltage is set equal to the second voltage. Ina step (F), the second voltage is altered by a voltage increment (whichmay be positive or negative) based on the magnitude and the polarity ofthe current difference. In a step (G), steps (A)-(F) are repeated duringoperation of the circuit to regulate operation of the loadnotwithstanding any changes in the electrical characteristics (e.g., thenon-linear current-voltage relationship) of the load during operation.

In another aspect, embodiments of the invention feature a method forcontrolling a circuit via application of first and second voltages. Thecircuit incorporates a load having electrical characteristics, which mayinclude or consist essentially of a non-linear current-voltagerelationship. In a step (A), the first voltage is applied to the load.In a step (B), a first current resulting from the first voltage appliedto the load is measured. In a step (C), the second voltage is applied tothe load. In a step (D), a second current resulting from the secondvoltage applied to the load is measured. A current difference betweenthe second current and the first current has a magnitude and a polarity.In a step (E), if the magnitude of the current difference is greaterthan a pre-determined value and the polarity of the current differenceis positive, the first voltage is set equal to the second voltage andthe second voltage is increased by a voltage increment. In a step (F),if the magnitude of the current difference is smaller than thepre-determined value and the polarity of the current difference isnegative, the first voltage is set equal to the second voltage and thesecond voltage is decreased by the voltage increment. In a step (G), ifthe magnitude of the current difference is greater than thepre-determined value and the polarity of the current difference isnegative, the first voltage is set equal to the second voltage and thesecond voltage is increased by the voltage increment. In a step (H), ifthe magnitude of the current difference is smaller than thepre-determined value and the polarity of the current difference isnegative, the first voltage is set equal to the second voltage and thesecond voltage is decreased by the voltage increment. In a step (I),steps (A)-(H) are repeated during operation of the circuit to regulateoperation of the load notwithstanding any changes in the electricalcharacteristics (e.g., the non-linear current-voltage relationship) ofthe load during operation.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The magnitude of the currentdifference may be greater than the pre-determined value, the secondvoltage may be increased above a maximum operating voltage, and thesecond voltage may be decreased to the maximum operating voltage or lessprior to applying the second voltage to the load. The maximum operatingvoltage may be approximately 60 V. The method may include pausing for apre-determined amount of time prior to applying the second voltage tothe load. The pre-determined amount of time may be selected from therange of approximately 10 milliseconds to approximately 3600 seconds.The pre-determined amount of time may increase as a number of timessteps (A)-(H) are repeated increases. The voltage increment may decreaseas a number of times steps (A)-(H) are repeated increases.

After a plurality of repetitions of steps (A)-(H), the circuit mayoperate at a stable operating range for at least a second plurality ofrepetitions of steps (A)-(H). As used herein, a “stable operating range”is a substantially unchanging range of voltages bounded by the first andsecond voltages; that is, the voltage applied to the load oscillatesbetween substantially constant first and second voltages, therebydefining the stable operating range. The stable operating range isgenerally constant while the current-voltage relationship of the load issubstantially constant; changes in the current-voltage relationship ofthe load may alter the stable operating range.

The method may include pausing for a pre-determined amount of time priorto applying the second voltage to the load, and the pre-determinedamount of time may increase at least once while the circuit operates atthe stable operating range. The pre-determined amount of time may bereset to a default value if circuit operation diverges from the stableoperating range. The voltage increment may be decreased at least oncewhile the circuit operates at the stable operating range. After thevoltage increment has been decreased, the voltage increment may bemaintained at a substantially constant value notwithstanding continuedcircuit operation at the stable operating range. The voltage incrementmay be reset to a default value if the circuit operation diverges fromthe stable operating range.

The load may include or consist essentially of a light-emitting array.The light-emitting array may include or consist essentially of first andsecond spaced-apart power conductors, a plurality of light-emittingstrings, and a plurality of control elements. Each light-emitting stringmay include or consist essentially of a plurality of interconnectedlight-emitting diodes spaced along the light-emitting string. A firstend of each light-emitting string may be electrically coupled to thefirst power conductor, and a second end of each light-emitting stringmay be electrically coupled to the second power conductor. The powerconductors may supply power to each of the light-emitting strings. Eachcontrol element may be electrically connected to at least onelight-emitting string and configured to utilize power supplied from thepower conductors to control the current to the at least onelight-emitting string to which it is electrically connected. Thelight-emitting diodes may emit substantially white light. The non-linearcurrent-voltage relationship of the load may include a knee (i.e., achange in slope), a stationary point (i.e., a local or absolute maximumor minimum), and/or an inflection point.

In yet another aspect, embodiments of the invention feature a controlsystem for operating a load via application of first and secondvoltages. The load may have electrical characteristics that may includeor consist essentially of a non-linear current-voltage relationship. Thecontrol system includes or consists essentially of a variable voltagesource, a sense element, and a controller. The controller is configuredto, in a step (A), apply, via the variable voltage source, the firstvoltage to the load, in a step (B), measure, via the sense element, afirst current resulting from the first voltage applied to the load, in astep (C), apply, via the variable voltage source, the second voltage tothe load, and in a step (D), measure, via the sense element a secondcurrent resulting from the second voltage applied to the load. A currentdifference between the second current and the first current has amagnitude and a polarity. The controller is further configured to, in astep (E), if the magnitude of the current difference is greater than apre-determined value and the polarity of the current difference ispositive, (i) set the first voltage equal to the second voltage and (ii)increase the second voltage by a voltage increment. The controller isfurther configured to, in a step (F), if the magnitude of the currentdifference is smaller than the pre-determined value and the polarity ofthe current difference is negative, (i) set the first voltage equal tothe second voltage and (ii) decrease the second voltage by the voltageincrement. The controller is further configured to, in a step (G), ifthe magnitude of the current difference is greater than thepre-determined value and the polarity of the current difference isnegative, (i) set the first voltage equal to the second voltage and (ii)increase the second voltage by the voltage increment. The controller isfurther configured to, in a step (H), if the magnitude of the currentdifference is smaller than the pre-determined value and the polarity ofthe current difference is negative, (i) set the first voltage equal tothe second voltage and (ii) decrease the second voltage by the voltageincrement. The controller is further configured to, in a step (I),repeat steps (A)-(H) during operation of the circuit to regulateoperation of the load notwithstanding any changes in the electricalcharacteristics (e.g., the non-linear current-voltage relationship) ofthe load during operation.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The load may have a non-linearcurrent-voltage relationship. The load may include or consistessentially of a plurality of light-emitting elements. The load mayinclude or consist essentially of a plurality of light-emitting stringseach including or consisting essentially of a plurality ofseries-connected light-emitting elements and at least onecurrent-control element. The at least one current-control element mayinclude or consist essentially of two transistors and two resistors. Thesense element may include or consist essentially of a resistor.

The load may include or consist essentially of a light-emitting array.The light-emitting array may include or consist essentially of first andsecond spaced-apart power conductors, a plurality of light-emittingstrings, and a plurality of control elements. Each light-emitting stringmay include or consist essentially of a plurality of interconnectedlight-emitting diodes spaced along the light-emitting string. A firstend of each light-emitting string may be electrically coupled to thefirst power conductor, and a second end of each light-emitting stringmay be electrically coupled to the second power conductor. The powerconductors may supply power to each of the light-emitting strings. Eachcontrol element may be electrically connected to at least onelight-emitting string and configured to utilize power supplied from thepower conductors to control the current to the at least onelight-emitting string to which it is electrically connected. Thelight-emitting diodes may emit substantially white light. The non-linearcurrent-voltage relationship of the load may include a knee, astationary point, and/or an inflection point.

In another aspect, embodiments of the invention feature a control systemfor operating a load via application of first and second voltages. Theload may have electrical characteristics that may include or consistessentially of a non-linear current-voltage relationship. The controlsystem includes or consists essentially of a variable voltage source, asense element, and a controller. The controller is configured to, in astep (A), apply, via the variable voltage source, the first voltage tothe load, in a step (B), measure, via the sense element, a first currentresulting from the first voltage applied to the load, in a step (C),apply, via the variable voltage source, the second voltage to the load,and in a step (D), measure, via the sense element a second currentresulting from the second voltage applied to the load. A currentdifference between the second current and the first current has amagnitude and a polarity. The controller is further configured to, in astep (E), set the first voltage equal to the second voltage, and in astep (F), alter (i.e., add to or subtract from) the second voltage by avoltage increment based on the magnitude and the polarity of the currentdifference. The controller is further configured to, in a step (G),repeat steps (A)-(F) during operation of the circuit to regulateoperation of the load notwithstanding any changes in the electricalcharacteristics (e.g., the non-linear current-voltage relationship) ofthe load during operation.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The controller may be configured toalter the second voltage by one or more of the following. If themagnitude of the current difference is greater than a pre-determinedvalue and the polarity of the current difference is positive, the secondvoltage is increased by the voltage increment. If the magnitude of thecurrent difference is smaller than the pre-determined value and thepolarity of the current difference is negative, the second voltage isdecreased by the voltage increment. If the magnitude of the currentdifference is greater than the pre-determined value and the polarity ofthe current difference is negative, the second voltage is increased bythe voltage increment. If the magnitude of the current difference issmaller than the pre-determined value and the polarity of the currentdifference is negative, the second voltage is decreased by the voltageincrement.

The load may include or consist essentially of a plurality oflight-emitting elements. The load may include or consist essentially ofa plurality of light-emitting strings each including or consistingessentially of a plurality of series-connected light-emitting elementsand at least one current-control element. The at least onecurrent-control element may include or consist essentially of twotransistors and two resistors. The sense element may include or consistessentially of a resistor. The non-linear current-voltage relationshipof the load may include a knee, a stationary point, and/or an inflectionpoint.

The load may include or consist essentially of a light-emitting array.The light-emitting array may include or consist essentially of first andsecond spaced-apart power conductors, a plurality of light-emittingstrings, and a plurality of control elements. Each light-emitting stringmay include or consist essentially of a plurality of interconnectedlight-emitting diodes spaced along the light-emitting string. A firstend of each light-emitting string may be electrically coupled to thefirst power conductor, and a second end of each light-emitting stringmay be electrically coupled to the second power conductor. The powerconductors may supply power to each of the light-emitting strings. Eachcontrol element may be electrically connected to at least onelight-emitting string and configured to utilize power supplied from thepower conductors to control the current to the at least onelight-emitting string to which it is electrically connected. Thelight-emitting diodes may emit substantially white light.

In another aspect, embodiments of the invention feature a method forcontrolling, via application of first and second voltages, a circuitincorporating a load having a non-linear current-voltage relationship.In a step (A), the first voltage is modulated in response to amodulation signal, thereby generating a first voltage waveform having afirst voltage level and a second voltage level. In a step (B), the firstvoltage waveform is applied to the load. In a step (C), a first currentresulting from the first voltage waveform applied to the load ismeasured. The first current is measured when the first voltage waveformis at the first voltage level. The first current may only be measuredwhen the first voltage waveform is at the first voltage level. In a step(D), the second voltage is modulated in response to the modulationsignal, thereby generating a second voltage waveform having a thirdvoltage level and a fourth voltage level. In a step (E), the secondvoltage waveform is applied to the load. In a step (F), a second currentresulting from the second voltage waveform applied to the load ismeasured. The second current is measured when the second voltagewaveform is at the third voltage level. The second current may only bemeasured when the second voltage waveform is at the third voltage level.A current difference between the second current and the first currenthas a magnitude and a polarity. In a step (G), the second voltage isaltered by a voltage increment having a magnitude and polarity based atleast in part on the magnitude and polarity of the current differencebetween the second current and the first current. In a step (H), steps(A)-(G) are repeated during operation of the circuit to regulateoperation of the load notwithstanding any changes in the non-linearcurrent-voltage relationship of the load during operation.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The first voltage waveform may includeor consist essentially of a series of voltage waves as a function oftime. One or more (e.g., all) of the voltage waves may include orconsist essentially of (i) a rising portion in which the voltageincreases from the second voltage level to the first voltage level, (ii)a center portion at the first voltage level, and (iii) a falling portionin which the voltage falls from the first voltage level to the secondvoltage level. One or more (e.g., all) of the voltage waves may includeor consist essentially of a substantially square wave having a minimumat the second voltage level and a maximum at the first voltage level.The modulation signal may change between step (A) and step (D). Thefirst voltage may be set equal to the second voltage after step (F).Step (g) may include or consist essentially of (i) if the magnitude ofthe current difference is greater than a pre-determined value and thepolarity of the current difference is positive, increasing the secondvoltage by the voltage increment, (ii) if the magnitude of the currentdifference is smaller than the pre-determined value and the polarity ofthe current difference is positive, decreasing the second voltage by thevoltage increment, (iii) if the magnitude of the current difference isgreater than the pre-determined value and the polarity of the currentdifference is negative, increasing the second voltage by the voltageincrement, and/or (iv) if the magnitude of the current difference issmaller than the pre-determined value and the polarity of the currentdifference is negative, decreasing the second voltage by the voltageincrement.

The second voltage may be increased above a maximum operating voltage,and the second voltage may be decreased to the maximum operating voltageor less prior to applying the second voltage waveform to the load. Theremay be a pause for a pre-determined amount of time prior to applying thesecond voltage waveform to the load. The pre-determined amount of timemay increase as a number of times steps (A)-(G) are repeated increases.The circuit may be configured to operate at a design point. The designpoint may include or consist essentially of a design current and/or adesign voltage. The voltage increment may be less than about 10% of thedesign voltage. The magnitude and polarity of the voltage increment maybe determined from (i) a comparison of a pre-determined value to themagnitude of the current difference between the second current and thefirst current and (ii) the polarity of the current difference betweenthe second current and the first current. The pre-determined value maybe constant as steps (A)-(G) repeat. The circuit may be configured tooperate at a design point, the design point including or consistingessentially of a design current and a design voltage, and thepre-determined value may be less than approximately 20% of the designcurrent. The pre-determined value may decrease as a number of timessteps (A)-(G) are repeated increases.

The load may include or consist essentially of a light-emitting array.The light-emitting array may include or consist essentially of first andsecond spaced-apart power conductors and a plurality of light-emittingstrings. At least one light-emitting string (i) may include or consistessentially of a plurality of interconnected light-emitting diodesspaced along the light-emitting string, (ii) may have a first endelectrically coupled to the first power conductor, and (iii) may have asecond end electrically coupled to the second power conductor. The powerconductors may supply power to each of the light-emitting strings. Thelight-emitting diodes may emit substantially white light. Thelight-emitting array may include a plurality of control elements. Atleast one control element may be (i) electrically connected to at leastone light-emitting string and (ii) configured to utilize power suppliedfrom the power conductors to control the current to the at least onelight-emitting string to which it is electrically connected.

The voltage increment may decrease as a number of times steps (A)-(G)are repeated increases. After a plurality of repetitions of steps(A)-(G), the circuit may operate at a stable operating range of voltagesfor at least a second plurality of repetitions of steps (A)-(G). Theremay be a pause for a pre-determined amount of time prior to applying thesecond voltage waveform to the load. The pre-determined amount of timemay increase at least once while the circuit operates at the stableoperating range. The pre-determined amount of time may be reset to adefault value if circuit operation diverges from the stable operatingrange. The voltage increment may be decreased at least once while thecircuit operates at the stable operating range. The magnitude and/orpolarity of the voltage increment may be determined from a table ofpre-determined rules. The non-linear current-voltage characteristic ofthe load may include a knee therewithin. The current may increase as thevoltage increases in the knee region. The current may decrease as thevoltage increases in the knee region. The non-linear current-voltagecharacteristic of the load may include a global minimum and/or a globalmaximum therewithin.

A first plurality of cycles of steps (A)-(G) repeating may constitute astart-up phase. A second plurality of cycles of steps (A)-(G) repeatingmay constitute an operation phase. The start-up phase may precede theoperation phase. During the start-up phase, the voltage increment maydecrease as a number of times steps (A)-(G) are repeated increases.During the operation phase, the voltage increment may decrease as anumber of times steps (A)-(G) are repeated increases. After the start-upphase, the circuit may operate at a stable operating range of voltagesfor at least a portion of the operating phase. The load may include orconsist essentially of a lighting system. An intensity of light emittedby the lighting system may be at least partially determined by a currentat which the lighting system operates. The non-linear current-voltagecharacteristic of the load may include a local minimum and/or a localmaximum therewithin. The modulation signal may include or consistessentially of a dimming signal.

In another aspect, embodiments of the invention feature a control systemfor operating a load via application of first and second voltages. Theload has a non-linear current-voltage relationship. The control systemincludes or consists essentially of a variable voltage source, a senseelement, a modulation controller, and a controller. The modulationcontroller is configured to (i) modulate the first voltage in responseto a modulation signal, thereby generating a first voltage waveformhaving a first voltage level and a second voltage level, and (ii)modulate the second voltage in response to the modulation signal,thereby generating a second voltage waveform having a third voltagelevel and a fourth voltage level. The controller is configured to (A)apply, via the variable voltage source and/or the modulation controller,the first voltage waveform to the load, (B) measure, via the senseelement, a first current resulting from the first voltage waveformapplied to the load, the first current being measured when the firstvoltage waveform is at the first voltage level, (C) apply, via thevariable voltage source and/or the modulation controller, the secondvoltage waveform to the load, (D) measure, via the sense element asecond current resulting from the second voltage waveform applied to theload, the second current being measured when the second voltage waveformis at the third voltage level, a current difference between the secondcurrent and the first current having a magnitude and a polarity, (E)alter the second voltage by a voltage increment based on the magnitudeand the polarity of the current difference, and (F) repeat steps (A)-(E)during operation of the circuit to regulate operation of the loadnotwithstanding any changes in the non-linear current-voltagerelationship of the load during operation.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The controller may be configured toset the first voltage equal to the second voltage after step (D). Thecontroller may be configured to alter the second voltage by (i) if themagnitude of the current difference is greater than a pre-determinedvalue and the polarity of the current difference is positive, increasingthe second voltage by the voltage increment, (ii) if the magnitude ofthe current difference is smaller than the pre-determined value and thepolarity of the current difference is positive, decreasing the secondvoltage by the voltage increment, (iii) if the magnitude of the currentdifference is greater than the pre-determined value and the polarity ofthe current difference is negative, increasing the second voltage by thevoltage increment, and/or (iv) if the magnitude of the currentdifference is smaller than the pre-determined value and the polarity ofthe current difference is negative, decreasing the second voltage by thevoltage increment. The non-linear current-voltage relationship of theload may include a knee therewithin. The load may include or consistessentially of a plurality of light-emitting elements. The load mayinclude or consist essentially of a plurality of light-emitting stringseach including or consisting essentially of a plurality ofseries-connected light-emitting elements and at least onecurrent-control element. The at least one current-control element mayinclude or consist essentially of two transistors and two resistors. Thesense element may include or consist essentially of one or moreresistors. The control system may include one or more switchescontrolled by the modulation controller to modulate the first voltageand/or the second voltage.

These and other objects, along with advantages and features of theinvention, will become more apparent through reference to the followingdescription, the accompanying drawings, and the claims. Furthermore, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. Reference throughout this specificationto “one example,” “an example,” “one embodiment,” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the example is included in at least one example ofthe present technology. Thus, the occurrences of the phrases “in oneexample,” “in an example,” “one embodiment,” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same example. Furthermore, the particular features,structures, routines, steps, or characteristics may be combined in anysuitable manner in one or more examples of the technology. As usedherein, the terms “substantially,” “approximately,” and “about”mean±10%, and in some embodiments, ±5%. The term “consists essentiallyof” means excluding other materials that contribute to function, unlessotherwise defined herein. Nonetheless, such other materials may bepresent, collectively or individually, in trace amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, with an emphasis instead generally being placedupon illustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1 is a circuit diagram of an illumination system;

FIG. 2A is a block diagram of a system in accordance with variousembodiments of the invention;

FIGS. 2B and 2C are partial circuit diagrams of illumination systems inaccordance with various embodiments of the invention;

FIGS. 3A-3H are graphs of current-voltage relationships of loads inaccordance with various embodiments of the invention;

FIGS. 4 and 5 are flowcharts of illumination system operation inaccordance with various embodiments of the invention;

FIGS. 6A, 6B, and 7 are circuit diagrams of illumination systems inaccordance with various embodiments of the invention;

FIGS. 8 and 9 are flowcharts of illumination system operation inaccordance with various embodiments of the invention;

FIG. 10 is a partial circuit diagram of an illumination system inaccordance with various embodiments of the invention;

FIG. 11 is a schematic diagram of circuitry of an illumination system inaccordance with various embodiments of the invention;

FIG. 12 is a schematic diagram of a portion of an illumination system inaccordance with various embodiments of the invention;

FIG. 13 is a schematic cross-section of a die attached to a substrate inaccordance with various embodiments of the invention;

FIG. 14A is a block diagram of a system in accordance with variousembodiments of the invention;

FIGS. 14B, 14C, 14D, 15A, and 15B are timing diagrams in accordance withvarious embodiments of the invention;

FIG. 16A is a block diagram of a system in accordance with variousembodiments of the invention;

FIGS. 16B and 17 are timing diagrams in accordance with variousembodiments of the invention;

FIG. 18 is a block diagram of a system in accordance with variousembodiments of the invention;

FIG. 19A is a schematic circuit diagram in accordance with variousembodiments of the invention;

FIGS. 19B and 19C are partial circuit diagrams in accordance withvarious embodiments of the invention; and

FIG. 20 is a block diagram of a system in accordance with variousembodiments of the invention.

DETAILED DESCRIPTION

FIG. 2A depicts an exemplary adaptive power system 200 in accordancewith embodiments of the present invention, although alternative systemswith similar functionality are also within the scope of the invention.As depicted, adaptive power system 200 includes or consists essentiallyof a variable voltage source 230, a sense element 210 and a controller220. Adaptive power system 200 is connected to a load 250 (e.g., one ormore LEEs or light-emitting strings). The controller 220, which embodiesprinciples of the present invention, directs variable voltage source 230to supply a specific voltage in response to a process embedded withincontroller 220 and the value of the current sensed by sense element 210,as will be discussed herein.

In one embodiment of the present invention, adaptive power system 200powers one or more light-emitting strings electrically coupled inparallel, where each light-emitting string includes or consistsessentially of one or more LEEs 110 electrically coupled in series witheach other and with a CCE 270, as shown in FIG. 2B. Referring to thestructure of FIG. 2B, a string 160 is equivalent to load 250 in FIG. 2A.The system shown in FIG. 2B includes or consists essentially of 20 LEEs110 in string 160; however, this is not a limitation of the presentinvention, and in other embodiments the number of LEEs 110 per string160 may be more or fewer than 20. Moreover, although the system shown inFIG. 2B includes one string 160, this also is not a limitation of thepresent invention, and in other embodiments more than one string 160 maybe utilized, for example in a parallel electrical configuration.

FIG. 2C shows a system similar to that of FIG. 2B, and illustrates oneembodiment of CCE 270. In the depicted embodiment, CCE 270 includes orconsists essentially of two resistors 285, 286 and two transistors 280,281 interconnected as shown in FIG. 2B. In general, CCEs may include oneor more passive components, such as resistors, capacitors, inductors, orfuses, as well as active components, e.g., transistors and diodes.

FIG. 3A shows a simulation of a string current 301 and a voltage 303across CCE 270 as a function of applied voltage for the system of FIG.2C. In this example the system includes 20 GaN-based LEEs 110 having aforward voltage in the range of about 2.6 V to about 3.1 V at a currentof about 5 mA. In this example the circuit is designed to control thestring current to about 5 mA; resistor 285 has a value of about 39kohms, resistor 286 has a value of about 113 ohms, and transistors 280and 281 may each be a MMBT2484 NPN general purpose amplifiermanufactured by Fairchild Semiconductor. If LEEs 110 have a nominalforward voltage of about 2.7 V, then the total voltage drop across all20 LEEs 110 is about 54 V. In order for the circuit to operate, theapplied voltage is at least about this value plus the voltage dropacross CCE 270. (As utilized herein, the “design point” is aproduct-wide, rather than individual device-specific, designatedoperating current (or operating voltage designed to achieve thedesignated current); actual individual devices may vary from the designpoint in operation. As utilized herein, the “relatively optimaloperating point” is the actual voltage required to achieve the desiredoperating current for a specific device at a specific time. Duringdevice operation the relatively optimal operating point may varytemporarily (e.g., due to temperature variations) or permanently (e.g.,due to aging).)

As may be seen from FIG. 3A, the circuit starts to turn on at about 52V, at which point the string current is about 2 mA. Increasing theapplied voltage above this level produces a relatively rapid increase incurrent and then, at the design point of 5 mA, the value of appliedvoltage levels off at about 55.8 V. At this point the applied voltage isabout 55.8 V, the voltage across CCE 270 is about 1.8 V, the voltageacross the 20 LEEs 110 is about 54 V, and the current through the LEEs110 is about 5 mA. As shown, operation of the circuit at appliedvoltages a small amount lower than or higher than the design pointresults in only small changes in the LEE 110 current. However, while thecurrent is relatively well controlled, the efficiency may decrease athigher applied voltages because the voltage drop across CCE 270 accountsfor a relatively larger portion of the overall voltage drop, whichresults in relatively more power dissipated as heat in this component.Thus, the efficiency decreases as the applied voltage is raised abovethe design point and, in preferred embodiments, the relatively optimaloperating point is the minimum applied voltage that just achieves thedesired current flow for a given device. One aspect of embodiments ofthe present invention is a system that automatically maintains therelatively optimal operating point. Specifically, the system maymaintain the relatively optimal operating point via oscillatingapplication of operating voltages that (1) are substantially constantover time (in the absence of temporary or permanent variations of theI-V characteristics of the devices of the load) and (2) bound therelatively optimal operating point within a stable operating range ofvoltages.

The operation of one embodiment of the invention may be understood inreference to FIG. 3A, which shows the load current 301 (current throughLEEs 110) and the voltage drop 303 across CCE 270 as a function ofapplied voltage.

With reference to FIGS. 2B, 3A, and 3B, in one embodiment, operation ofthe system of FIG. 2B begins at the voltage at point 310, designated asV₃₁₀. The current at this point is measured and designated as I₃₁₀. Thevoltage is then incremented to the voltage indicated by point 320,giving a voltage V₃₂₀ and a current I₃₂₀. The magnitude and sign of thedifference between I₃₂₀ and I₃₁₀ is then measured. If the magnitude ofthe difference is larger than a pre-determined value DI, and the sign ofI₃₂₀−I₃₁₀ is positive, then the system increments the voltage once againto point 330, producing voltage V₃₃₀ and current I₃₃₀. The magnitude andsign of the difference between I₃₃₀ and I₃₂₀ is again measured. If themagnitude of the difference is larger than a pre-determined value, andthe sign of I₃₃₀−I₃₂₀ is positive, then the system increments thevoltage once again to point 340, producing voltage V₃₄₀ and currentI₃₄₀. The magnitude and sign of the difference between I₃₄₀ and I₃₃₀ isagain measured. In this case the difference between I₃₄₀ and I₃₃₀ isless than a pre-determined value, but the sign is still positive, so thesystem does not increment the voltage further. Instead, the systemdecrements the voltage, for example back to V₃₃₀ at the point 330. In astable system, the decrement back to V₃₃₀ will typically result in acurrent of I₃₃₀. The magnitude and sign of the difference between I₃₄₀and I₃₃₀ is measured. In this example the difference between I₃₄₀ andI₃₃₀ is less than the preset value, but the sign is negative, so thesystem decrements the voltage once more to point 320, where, typicallyin a stable system the voltage is V₃₂₀ and the current is I₃₂₀. Now thedifference between I₃₂₀ and I₃₃₀ is determined and, again in a stablesystem, found to be larger than the pre-determined value. Also the signis negative, so the system knows that it has gone too far and incrementsthe applied voltage, for example back to V₃₃₀ where the current is I₃₃₀.

A table of rules for various embodiments of the present invention isshown in Table 1. Table 1 shows the direction of the voltage change(increment or decrement) as a function of the magnitude and sign of thedifference between the two measured currents. As may be understood bythis description, the voltage then steps back and forth around thedesign point 330, e.g., up to 340 and down to 320. FIG. 3A may beutilized to illustrate an exemplary embodiment of the present inventionin which the system maintains the relatively optimal operating point viaoscillating application of operating voltages that (1) are substantiallyconstant over time (in the absence of temporary or permanent variationsof the I-V characteristics of the devices of the load) and (2) bound therelatively optimal operating point within a stable operating range ofvoltages. The operation may be described from any starting point; here,starting with operating point 320, the system has just decrementeditself from operating point 330. This operation is identified as Phase Ain the phase cycle detailed below.

Phase A. At this point the operating point has just changed from point330 to point 320 (i.e., the voltage has just decremented from V₃₃₀ toV₃₂₀). I₃₂₀−I₃₃₀ is evaluated and the determination is made that thesign (i.e., the polarity) is negative and the magnitude is greater thanthe predetermined value. As Table 1 indicates, rule 4 is then applied toincrement the voltage to operating point 330.

Phase B. At this point the operating point has just changed from point320 to point 330. I₃₃₀−I₃₂₀ is evaluated and the determination is madethat the sign is positive and the magnitude is greater than thepredetermined value. As Table 1 indicates, rule 1 is then applied toincrement the voltage to operating point 340.

Phase C. At this point the operating point has just changed from point330 to point 340. I₃₄₀−I₃₃₀ is evaluated and the determination is madethat the sign is positive and the magnitude is less than thepredetermined value. As Table 1 indicates, rule 2 is then applied todecrement the voltage to operating point 330.

Phase D. At this point the operating point has just changed from point340 to point 330. I₃₃₀−I₃₄₀ is evaluated and the determination is madethat the sign is negative and the magnitude is less than thepredetermined value. As Table 1 indicates, rule 3 is then applied todecrement the voltage to operating point 320.

Phase D then leads back to Phase A, and the cycle continues in theabsence of a change in the I-V relationship of the load. This willtypically continue until there is a change in the system that modifiesthe current-voltage relationship, for example a shift in the curve, asdescribed herein. Evaluation of the change in current for variouschanges in voltages results in the determination of and setting ofrelatively optimal operating point. This process may proceed not onlyduring start-up of the system, but also during operation, such that anychanges induced by environmental factors, aging, or the like areautomatically accommodated. If the I-V relationship changes at any pointin the cycle, the magnitude and sign of the current difference willresult in application of an appropriate rule to bring the system back tothe relatively optimal operation point defined by the new I-Vrelationship.

TABLE 1 I₂ − I₁ Magnitude compared to Rule pre-determined value Sign ofdifference Voltage Change 1 Greater + Increment 2 Smaller + Decrement 3Smaller − Decrement 4 Greater − Increment

In preferred embodiments, the I-V relationship is non-linear. In someembodiments, the non-linear I-V relationship is characterized by a knee(i.e., a change in slope), stationary point (i.e., a local maximum orminimum), saddle point, or inflection point at or near the relativelyoptimal operating point. In one embodiment, the knee region may becharacterized by a change in the magnitude of the slope, while aninflection point may be characterized by a change in the sign (polarity)of the slope. In the example discussed in reference to FIG. 3A, the kneeis in the region of operating points 320, 330, and 340, and the slope ofthe I-V curve below the knee (at lower operating voltages) is higherthan the slope above the knee (at higher operating voltages). Thus, whenapplied, the rules in Table 1 drive the operating point to the kneeregion (the relatively optimal operating point) in response to thedifferent slope values above and below the relatively optimal operatingpoint. In other words, when the slope value decreases, the system isabove the relatively optimal operating point and when the slope valueincreases, the system is below the relatively optimal operating point.

It should be understood that this approach may be generalized beyond theexamples discussed in reference to FIGS. 3A and 3B and Table 1. FIGS.3C-3E show additional examples of non-linear I-V relationships andrelatively optimal operation points 391. For example, the I-Vrelationship shown in FIG. 3C is similar to that shown in FIG. 3A, butin this case the slope of the I-V curve below the knee (at loweroperating voltages) is less than the slope above the knee (at higheroperating voltages).

While FIGS. 3A-3E show examples having a knee region, this is not alimitation of the present invention, and in other embodiments otherfeatures may be used to identify the relatively optimal operating point.FIGS. 3F and 3G show two examples, where the relatively optimaloperating point 391 corresponds to a peak and a valley respectively(i.e., to stationary points). At these points the polarity of the slopechanges sign. In other words, the curve changes from being concave up toconcave down. The polarity of the slope of the I-V relationship shouldnot be confused with the sign of the difference in Table 1. The sign ofthe difference in Table 1 refers to the sign of the difference ofcurrents and is used as part of the determination to increment ordecrement the applied voltage.

While FIGS. 3A-3G show examples that have one feature defining therelatively optimal operating point, this is not a limitation of thepresent invention, and in other embodiments the I-V relationship mayhave more than one possible knee, stationary point, or inflection point,such as points 391, 392, 393 in FIG. 3H. In this case additional rulesmay be configured to distinguish the different and/or desired operatingpoints, for example including rules based on the absolute or relativemagnitudes of the current value. The examples shown in FIGS. 3A-3H arenot meant to be limiting, and the methods and systems described hereinmay be applied to systems characterized by a non-linear I-Vrelationship.

While the discussion above has been in reference to the I-V curve of anelectrical load, this approach may be applied to other control systems,where the parameters are not the applied voltage and resulting currentdetermined from the I-V relationship. In other words, the methods andsystems described herein may be applied to systems characterized by anon-linear load curve that defines the relationship of one or moreinputs and one or more responses. For example, other types of systems orrelationships that the present invention may be applied to include (a) aposition control system, where the response is the position and theinput is a signal to adjust the position, (b) a pressure control system,for example to apply and control pressure in a mold, reaction chamber orthe like, where the response is the pressure and the input is the signalto adjust the pressure, (c) a temperature control system, where theresponse is the temperature and the input is the signal to adjust thepressure, (d) a humidity control system, where the response is thehumidity and the input is the signal to adjust the humidity, (e) a flowcontrol system, where the response is the flow of a fluid and the inputis the signal to adjust the flow, (f) a lighting control system, wherethe response is a lighting characteristic such as intensity, luminance,illuminance, color temperature, or the like, and the input is the signalto adjust the lighting characteristic.

In general, the approach to applying embodiments of the presentinvention is to determine the load relationship (between one or moreinputs and one or more outputs), determine the relatively optimaloperating point and determine a set of rules based on changes to theinput(s) to drive the system to its relatively optimal operating point.The rules may then be embodied in hardware and/or software or othermeans to effect changes in the system and provide control to therelatively optimal operating point. As stated herein, an advantage ofthis is that in preferred embodiments it provides automatic optimizationto the relatively optimal operating point for a distribution of systems,where the relatively optimal operating point may vary because ofvariations in component values, aging, environmental conditions, or thelike.

The value of DI, the predetermined current difference value, may beinfluenced by a number of factors. For example, in one embodiment, DImay be set to a relatively small value in order to result in arelatively small range of operation about the operating point. Forexample, in the system described in reference to FIGS. 2 and 3A, DI maybe less than about 1 mA, or less than about 0.5 mA, or less than about0.1 mA. In some embodiments DI may be less than 20% of the value of thecurrent at the operating point, or less than about 10% of the value ofthe current at the operating point, or less than about 2% of the valueof the current at the operating point. However, the specific value of DIis not a limitation of the present invention, and in other embodimentsDI may have any value.

As shown in FIG. 3A, the current-voltage curve may have a knee or bendin it, i.e., the region near points 320, 330, and 340. While point 330identifies the 5 mA design point, it is important to note that thevoltage value at which this occurs may be different for differentlight-emitting strings, either within the system or between differentsystems, resulting, for example, from manufacturing and/or operationalvariations. A key aspect of some embodiments of this invention is theuse of the signature of the I-V curve of the load to determine andoperate at a relatively optimal operating point. While FIG. 3A shows oneexample of an I-V curve, the shape or current or voltage valuesassociated with the I-V curve shown in FIG. 3A are not limitations ofthe present invention, and in other embodiments the I-V curve may haveany shape.

FIG. 3A shows how an embodiment of the present invention operates in astable regime, where in this context stable means that the I-V curve isrelatively fixed and does not shift or change shape. However, in someembodiments, the system may not be stable. For example, manufacturingvariations may result in different I-V relationships for differentversions of the same system, for example, because of variations incomponent values within the system. Also, the I-V relationship maychange with time, for example as a result of changes in operatingconditions (e.g., sudden or frequent system on/off cycles),environmental factors such as temperature, aging, component failure, orthe like. Embodiments of the present invention accommodate thesevariations and operate at the relatively optimal operating point.

In the example of a light-emitting system, in some embodiments the curverelating operating current to applied voltage may shift to the left orright, while maintaining essentially the same shape. For example,components such as LEDs have manufacturing tolerances and there may be adistribution in characteristics (e.g., forward voltage) over themanufacturing output. This means that the sum of the forward voltage ofall of the LEEs in different light-emitting strings may have differentvalues, and thus a different minimum applied voltage may be required toachieve the desired current flow. For example, if the sum of the forwardvoltage of all of the LEEs in different light-emitting stringsincreases, then the minimum applied voltage to achieve the desiredcurrent increases. Conversely, if the sum of the forward voltage of allof the LEEs in different light-emitting strings decreases, then theminimum applied voltage to achieve the desired current decreases.

In addition to manufacturing tolerances (e.g., on all components in thesystem, for example the components making up CCE 270, not just LEEs),operational variations may also change the value of the string voltage(where the string voltage includes or consists essentially of the sum ofthe forward voltage of all of the LEEs in a light-emitting string aswell as the voltage drop across CCE 270 and any other elements that maybe in the light-emitting string). For example, as the temperaturedecreases, in embodiments where LEEs 110 include or consist essentiallyof LEDs, the forward voltage of LEEs 110 may increase. Thus in someembodiments, as the temperature decreases, the minimum applied voltageto achieve the desired current increases.

FIG. 3B shows three I-V relationships for a lighting system. Curve 302illustrates the same relationship as the curve in FIG. 3A. Curve 306shows an example of an I-V relationship where the string voltage isrelatively smaller than that for curve 302 while curve 308 shows anexample of an I-V relationship where the string voltage is relativelylarger than that for curve 302.

If the system is initially operating at point 330 on curve 302 and thereis a change in operational parameters to curve 308, the voltageinitially remains at V₃₃₀; however, the current decreases to thatassociated with point 360 on curve 308 and the system is not operatingat the relatively optimal operating point. At the next voltage incrementtime the system will act to move the voltage back to the relativelyoptimal operating point, which for curve 308 is point 370, in a mannersubstantially the same as described in reference to FIG. 3A.

If the system is initially operating at point 330 on curve 302 and thereis a change in operational parameters to curve 306, the voltage remainsat V₃₃₀; however, the current increases to that associated with point390 on curve 306 and the system is not operating at the relativelyoptimal operating point. At the next voltage increment time the systemwill act to move the voltage back to the relatively optimal operatingpoint, which for curve 306 is point 380, in a manner substantially thesame as described in reference to FIG. 3A.

As discussed herein, in some embodiments such operational changes mayresult from environmental factors, such as a change in ambienttemperature due to weather, heating or air conditioning systems, or thelike. For example, systems may be installed in different environmentshaving relatively well controlled, but different ambient temperatures,such as in an office space or home, or in a freezer case. Alternately,systems may be installed in different environments where the temperatureis not well controlled, for example non-climate controlled warehouses,outdoor lighting, etc. In other situations the I-V curve may shiftbecause of self-induced effects. For example, when a system is off, itmay have a temperature close to that of the ambient temperature. When itis turned on, the various components begin to heat up, raising theirtemperature and possibly shifting the I-V curve. Where the systemincludes LEDs, the forward generally voltage drops as the LEDs heat up,resulting in a shift of the I-V curve, for example from that of curve308 to curve 302 in FIG. 3B. In other situations, manufacturingvariations in the actual value of component parts, for example LEEs 110and/or the components of CCE 270, may result in a range of I-V curvepositions and shapes, for the complete manufacturing distribution of thesystem.

FIG. 4 depicts a flowchart of an exemplary process 400 in accordancewith various embodiments of the invention. Process 400 is shown havingeleven steps; however, this is not a limitation of the presentinvention, and in other embodiments the invention has more or fewersteps and/or the steps may be performed in different order. In step 410,a voltage V1 is applied to the load. In step 415, the current I1, for anapplied V1, is measured. In step 415, the voltage V1 is incremented tovoltage V2. In step 420, the voltage V2 is applied to the load. In step425, the current I2, for an applied V2, is measured. In step 430, thecurrent I2 is compared to current I1. In step 435, a decision is madewhether to increment or decrement the voltage, for example based on therules of Table 1. If the decision is to increment the voltage, theprocess moves to step 450. In step 450, the value of current I1 is setto the value of current I2 (note that this step is for calculation orcomparison purposes and is not physically setting a current value in theactual system). In step 455, the voltage V2 is incremented. After step455, the process returns to step 420 where the new value of V2 isapplied to the load, a new value of current I2 is measured (step 425)and the difference between the new values of current I2 and current I1(which is the previous current I2 value) is determined (step 430). If instep 435 the decision is to decrement the voltage, the process moves tostep 440. In step 440, the value of current I1 is set to the value ofcurrent I2. In step 455, voltage V2 is decremented. After step 445, theprocess returns to step 420 where the new value of voltage V2 is appliedto the load, a new value of current I2 is measured (step 425) and thedifference between the new value of current I2 and current I1 (which isthe previous current I2 value) is determined (step 430). Note that invarious embodiments it is not necessary to know (or measure) the exactvalue of the applied voltage after the system is started up, as the nextapplied voltage is modified relative to its previous value withoutmeasurement of its actual value.

In some embodiments of process 400, the system starts with an initialvoltage V1 that is known to be below the desired operating voltagepoint, for example point 310 in FIG. 3A. In this way the system may beconfigured to not exceed a certain operating voltage limit. For examplea UL Class 2 certification requires the operating voltage to not exceed60 V under operating conditions. By starting the system with voltageV1<60 V this requirement may be satisfied. An additional step, forexample just prior to step 420 may include a check to ensure that theapplied voltage is less than a certain value, for example 60 V in a ULClass 2 system. For example, FIG. 5 shows one embodiment of an optionalstep to check the value of the voltage to be applied. In someembodiments this step 510 may be positioned just prior to step 420 inFIG. 4. (A similar check may also be made before step 410, uponinitialization of the system, if desired.) In step 510, the value of thevoltage V2 to be applied is compared to a maximum allowable value. Forexample in some embodiments of a UL Class 2 system where the maximumallowable voltage is 60 V, V_(MAX) may be set to a value slightly lessthan 60 V, for example 59 V or 58 V or 57 V or the like. If the value ofthe voltage V2 that is to be applied is less than V_(MAX) the processproceeds normally. If the value of the voltage V2 that is to be appliedis equal to or larger than V_(MAX) the process moves to a differentbranch. Depending on the design, various actions may be taken. In oneembodiment, the value of voltage V2 is limited to V_(MAX) or some othervalue less than V_(MAX). In one embodiment, the system is instructed toshut down. The action taken upon voltage V2 being larger than V_(MAX) isnot a limitation of the present invention.

As will be understood from the description herein, a key aspect of someembodiments of this invention is that it is not necessary to know,either in advance or in real time, the “desired” applied voltage. Thesystem uses the I-V signature to determine the relatively optimalapplied voltage without knowing its specific value.

Referring back to FIG. 2A, an example of a block diagram of a circuitembodying the principles of the present invention is shown. As will beunderstood by those skilled in the art, there are many types orconfigurations of variable voltage sources that may be used for variablevoltage source 230 in FIG. 2A. FIG. 6A shows a circuit block diagram ofone exemplary embodiment of the present invention that includes aflyback switching power supply. The circuit in FIG. 6A includes orconsists essentially of a bridge rectifier 610, a switching andisolation transformer 620, a switching power supply controller 630,switching MOSFET 635, an optoisolator (or “optical isolator”) 640, andan adaptive controller 650. In one embodiment, the circuit operates asfollows; adaptive controller 650 determines the voltage to be applied toa load 660. A signal is sent from adaptive controller 650 throughoptoisolator 640 to switching power supply controller 630 to set thevoltage applied to load 660 to the desired value. Switching power supplycontroller 630 sets the modulation frequency of switching MOSFET 635,driving the duty cycle of switching and isolation transformer 620 andresulting in the desired voltage being applied to load 660. The loadcurrent is measured by means of a shunt resistor 655. The adaptivecontroller follows a process to adjust to a relative optimum outputvoltage, as discussed herein, for example in relationship to thedescription of FIG. 4 and/or Table 1.

FIG. 6B shows an example of an embodiment of the circuit block diagramof FIG. 6A in which adaptive controller 650 includes or consistsessentially of a microcontroller 670. In one embodiment, microcontroller670 reads the applied current by means of shunt resistor 655 (through anoptional multiplexer) and an analog to digital (A/D) converter within orexternal to microcontroller 670. Microcontroller 670 outputs an analogsignal by means of a digital to analog (D/A) converter (within orexternal to microcontroller 670), which is representative of the desiredapplied voltage. This analog signal is applied to optoisolator 640 toset the desired output voltage to the load 660. Microcontroller 670 isprogrammed, for example in software or firmware, to carry out thedesired process, for example that in relation to FIG. 4 and/or Table 1.

The microcontroller 670 may be a general-purpose microcontroller, butdepending on implementation may alternatively be a microprocessor,peripheral integrated circuit element, a customer-specific integratedcircuit (CSIC), an application-specific integrated circuit (ASIC), alogic circuit, a digital signal processor, a programmable logic devicesuch as a field-programmable gate array (FPGA), a programmable logicdevice (PLD), a programmable logic array (PLA), an RFID processor, smartchip, or any other device or arrangement of devices that is capable ofimplementing the steps of the processes of embodiments of the invention.Moreover, some of the functions of microcontroller 670 may beimplemented in software and/or as mixed hardware-software modules.Software programs implementing the functionality herein described may bewritten in any of a number of high level languages such as FORTRAN,PASCAL, JAVA, C, C++, C#, BASIC, various scripting languages, and/orHTML. Additionally, the software may be implemented in an assemblylanguage directed to microcontroller 670. The software may be embodiedon an article of manufacture including, but not limited to, a floppydisk, a jump drive, a hard disk, an optical disk, a magnetic tape, aPROM, an EPROM, EEPROM, field-programmable gate array, CDROM, or DVDROM.Embodiments using hardware-software modules may be implemented using,for example, one or more FPGA, CPLD, or ASIC processors.

FIG. 7 shows an example of an embodiment of the circuit block diagram ofFIG. 6A in which adaptive controller 650 includes or consistsessentially of an analog circuit 780. Also shown in FIG. 7 is anoptional power factor correction stage 715 and an optional rectificationand smoothing stage 725. The embodiment shown in FIG. 7 also shows threeswitching transistors 635, 635′, and 635″; however, this is not alimitation of the present invention, and in other embodiments fewer ormore switching transistors 635 may be utilized. In some embodiments,these are controlled by switching controller 630. In the depictedembodiment, the value of the load current is sampled across shuntresistor 655 by two conventional sample-and-hold circuits 781, 782. Thesample-and-hold circuits sample the load current alternately, the timingof the alternate sampling being controlled by sample-and-hold controller783. The difference between the two current levels sampled at successivetimes is determined by a comparator 784 and sent to an integrator 785that drives optoisolator 640. In operation, the comparator 784determines the difference between the successive current values measuredby sample-and-hold circuits 781, 782. In some embodiments, a smalloffset, delta 786, is added to (via, e.g., a voltage adder) the value ofthe output of sample-and-hold 781. In some embodiments, delta 786 servesthe same purpose as the predetermined value DI as discussed herein. Thedifference between [sample-and-hold 781+delta 786] and sample and hold782 is sent to comparator 784. If [sample and hold 781+delta 786] isgreater than sample-and-hold 782, or if sample-and-hold781−sample-and-hold 782 is greater than delta 786, the output ofcomparator 784 is positive, which then drives integrator 785 outputpositive, which increases the voltage to load 660. If [sample-and-hold781+delta 786] is less than sample-and-hold 782, or if sample-and-hold781−sample-and-hold 782 is less than delta 786, the output of comparator784 is negative, which then drives integrator 785 output negative, whichdecreases the voltage to load 660. In this way, if the change in loadcurrent from one sample period to the next is greater than delta 786,the voltage is changed. If the change in load current from one sampleperiod to the next is less than delta 786, integrator 785 drives theload voltage lower, such that at the next or successive samplinginterval, the change in load current between sample periods is greaterthan delta 786, driving the voltage back up. In this way the loadvoltage oscillates around the relative optimal operating point.

The systems shown in FIGS. 6A-6C and FIG. 7 show two embodiments ofcircuits that may be used to embody elements of the present invention,although alternative systems with similar functionality are also withinthe scope of the invention. As will be understood by those skilled inthe art, there are many electrical topologies for switching powersupplies, and the specific topology of the power supply is not alimitation of the present invention.

As will be recognized from the description in reference to FIGS. 3A and4, in some embodiments once the system is near its relative optimaloperating point and the I-V relationship is substantially stable, theadaptive power system may cycle back and forth about the relativeoptimal operating point. For example, in the example in reference toFIG. 3A, the operating point cycles between points 320 and 340 throughpoint 330. In some embodiments, a fixed or variable wait time may beadded to the process, for example the process shown in reference to FIG.4, to reduce the cycle frequency. FIG. 8 is a flowchart of an exemplaryprocess 800 in accordance with various embodiments of the invention.Process 800 is similar to process 400 shown in FIG. 4, with theinclusion of a wait step 810 just before step 420, Apply V2. Process 800is shown having twelve steps; however, this is not a limitation of thepresent invention, and in other embodiments the invention has more orfewer steps and/or the steps may be performed in different order. Insome embodiments, wait step 810 may be fixed, for example wait step 810may range from about 10 milliseconds (ms) to about 10 seconds, althoughthe specific value of a fixed wait time is not a limitation of thepresent invention. In some embodiments, wait step 810 may be variable.For example, in some embodiments wait step 810 may be relatively shortduring start-up of the system and may increase with time. For example,in some embodiments wait step may have a value between about 1 ms andabout 100 ms during the start-up time and may have a wait step valuebetween about 100 ms and about 1 hour or 1 day or more during operation.In some embodiments, the start-up period may be in the range of about 10seconds to about 5 minutes (from start-up of the system). However, thewait times during start-up and operation, as well as the start-up periodare not limitations of the present invention, and in other embodimentsthese may have any value. In some embodiments, these values may be inpart determined by system characteristics and in part by ambientconditions. For example, the start-up period in some embodiments may bedetermined in part by the time required for the system to thermallystabilize after being turned on.

In some embodiments, the ΔV voltage increment may be fixed while inother embodiments the ΔV increment may be variable. In some embodiments,the ΔV increment may be in the range of about 0.05 V to about 5 V;however, the ΔV increment value is not a limitation of the presentinvention. In some embodiments, the ΔV increment is determined as apercentage of the operating voltage. For example, ΔV may be in the rangeof about 10% of the operating voltage to about 0.01% of the operatingvoltage; however, the ΔV increment value as a percentage of theoperating voltage is not a limitation of the present invention. In someembodiments, the ΔV increment may be relatively small during start-up ofthe system and may increase with time. For example, in some embodimentsthe ΔV increment may have a value between about 0.05 V and about 0.25 V(or between about 0.01% to about 0.5% of the operating voltage) duringthe start-up time and may have a ΔV increment value between about 0.25 Vand about 1 V (or between about 0.5% to about 2% of the operatingvoltage) during operation. In some embodiments, the ΔV increment mayhave a value between about 0.25 V and about 1 V (or between about 0.5%to about 2% of the operating voltage) during the start-up time and mayhave a ΔV increment value between about 0.05 V and about 0.25 V (orbetween about 0.01% to about 0.5% of the operating voltage) duringoperation. In some embodiments the start-up period may be in the rangeof about 10 seconds to about 5 minutes (from start-up of the system).However, the wait times during start-up and operation, as well as thestart-up period, are not limitations of the present invention, and inother embodiments these may have any value. In some embodiments, thesevalues may be in part determined by system characteristics and in partby ambient conditions. For example, the start-up period in someembodiments may be determined in part by the time required for thesystem to thermally stabilize (i.e., reach an approximately constanttemperature given ambient conditions and heat generated by the systemitself) after being turned on.

In some embodiments, the pre-determined value DI used to evaluate thecurrent difference I₂−I₁ may be fixed, while in other embodiments it maybe variable. In some embodiments, the pre-determined value DI used toevaluate I₂−I₁ may be in the range of about 0.01 mA to about 1 mA;however, the pre-determined value DI used to evaluate I₂−I₁ is not alimitation of the present invention. In some embodiments, DI may beabout or less than 20% of the value of the current at the operatingpoint, or about or less than about 10% of the value of the current atthe operating point, or about or less than about 2% of the value of thecurrent at the operating point. However, the specific value of DI is nota limitation of the present invention, and in other embodiments DI mayhave any value.

For example, in some embodiments the pre-determined value used toevaluate the current difference I₂−I₁ may be variable. For example inone embodiment, the current difference I₂−I₁ may be relatively smallduring start-up of the system and may increase with time. For example,in some embodiments the pre-determined value used to evaluate I₂−I₁ mayhave a value between about 0.1 mA and about 1 mA during the start-uptime and may have a value between about 0.01 mA and about 0.1 mA duringoperation. In some embodiments, the start-up period may be in the rangeof about 10 seconds to about 5 minutes (from start-up of the system).However, the pre-determined value used to evaluate I₂−I₁ during start-upand operation, as well as the start-up period, are not limitations ofthe present invention, and in other embodiments these may have anyvalue. In some embodiments, these values may be in part determined bysystem characteristics and in part by ambient conditions. For example,the start-up period in some embodiments may be determined in part by thetime required for the system to thermally stabilize after being turnedon. Table 2 shows an example of a two-level system with differentpossibilities of the wait time, ΔV increment and/or pre-determined valueused to evaluate I₂−I₁ for two different periods, start-up andoperation. The values discussed with respect to this example and inconnection with Table 2 are exemplary values; the specific values arenot limitations of the present invention.

TABLE 2 Pre-determined Period Wait Time (s) ΔV increment (V) I2 − I1value (mA) Start-up 0.001-0.1 0.05-0.25  0.1-1.0 Operation     0.1-36000.25-1.0  0.01-0.1

While the discussion above relative to different wait times, ΔVincrements, and the pre-determined value used to evaluate I₂−I₁ has beenwith reference to a two-level system (that is a system with two periodshaving different characteristics), this is not a limitation of thepresent invention, and in other embodiments more than two levels may beutilized. While the discussion above relative to two or more periods hasbeen with reference to wait times, ΔV increments, and the pre-determinedvalue used to evaluate I₂−I₁, this is not a limitation of the presentinvention, and in other embodiments other parameters may have differentvalues during these periods as well. In some embodiments, only one orseveral parameters have different values during different periods.

In some embodiments, various adaptive parameters may have discretevalues, while in other embodiments they may vary continuously. Here“adaptive parameters” are parameters that control or direct theoperation of the adaptive power supply system including but not limitedto wait times, ΔV increments, and the pre-determined value used toevaluate I₂−I₁.

In some embodiments, adaptive parameters may be changed dynamically,that is for example in response to various states of the process, asopposed to being changed by time period, as discussed above. Forexample, FIG. 9 depicts a flowchart of an exemplary process 900 inaccordance with various embodiments of the invention. Process 900 issimilar to process 800 shown in FIG. 8; however, in process 900 one ormore parameters (for example Wait Time, ΔV, DI) may be changed based ona determination in an adjust-parameter step 910. For example, in anembodiment in which the system is relatively stable and is cycling backand forth around a central current-voltage point, as described inreference to FIG. 3C, step 910 may count how many times the system hascycled back and forth around substantially the same points. When thecycle count reaches a maximum, the wait time may be changed, for exampleincreased, to reduce the amount of cycling. In another example, when thesystem is relatively stable, the value of ΔV may be reduced to moreclosely approach the relatively optimal operating point. In anotherexample, DI may be changed. For example, DI/ΔV may be considered to be ameasure of the slope of the I-V relationship, and in some embodiments,DI may be modified to improve the operation of process 900, for exampleto better match the measured change in current as a response to ΔVchanges to the slope of the I-V curve. The forgoing examples are for arelatively stable system. If there is a shift in the systemrelationship, for example as described in reference to FIG. 3B, thenthere is a disruption in the response cycle described in reference toFIG. 3C and in some embodiments, in step 910 one or more parameters areset to their default value or set to another value dependent on thenature and extent of the disruption. The number and function of thesteps shown in process 900 is exemplary and are not a limitation of thepresent invention, and in other embodiments the invention has more orfewer steps and/or the steps may be performed in different order.

EXAMPLE 1

In this example, the number of stable cycles (shown in FIG. 3C) iscounted. For every X cycles around a relatively stable operating point(X is an integer, for example 10, 50, 100, or another number), the waittime increases. For example, in one embodiment the wait time may doubleafter X cycles. Taking the case where X is 50, if the system cycles 50times around the operating point in a relatively stable fashion, thewait time doubles. If it cycles another 50 times around the operatingpoint in a relatively stable fashion, the wait time doubles again (4×the original value). As long as the system is stable, the wait timeincreases, reducing the cycle frequency. If the system detects adifferent pattern (e.g., current-voltage relationship), then step 910sets the wait time back to the starting default value. In the examplesbelow, the specific values are representative and other values may beused.

EXAMPLE 2

In this example, the number of stable cycles (shown in FIG. 3C) iscounted. For every X cycles around a relatively stable operating point(X is an integer, for example 10, 50, 100, or another number), ΔV isdecreased. For example, in one embodiment the ΔV is decreased by 10%,25%, 50%, or some other amount. Taking the case where X is 50 and the ΔVdecrease is 10%, if the system cycles 50 times around the operatingpoint in a relatively stable fashion, then ΔV is set to 0.9ΔV. If itcycles another 50 times around the operating point in a relativelystable fashion, ΔV decreases again to 0.81ΔV. As long as the system isstable, ΔV decreases. This permits the system to take finer and finervoltage steps to more closely approach the relatively optimal operatingpoint. In most embodiments, it is preferable to set a minimum ΔV value.If the system detects a different pattern (e.g., current-voltagerelationship), then step 910 sets ΔV back to the starting default value.

EXAMPLE 3

In this example the number of stable cycles (shown in FIG. 3C) iscounted. For every X cycles around a relatively stable operating point(X is an integer, for example 10, 50, 100, or another number), ΔV isdecreased until a minimum ΔV value is reached, for example 5 cycles ofmonotonic ΔV reduction. After that, as long as the system is stable, thewait time is then increased. For example, in one embodiment the ΔV maybe decreased by 10% in each of 5 steps. Thus, in a relatively stablesystem the ΔV values are ΔV, 0.9ΔV, 0.81ΔV, 0.73 ΔV and 0.66ΔV. If thesystem goes through 5 cycles of monotonic ΔV reduction, the value of ΔVwill be 0.59ΔV and will remain fixed as long as the system is stable. Ifthe system is stable for another 50 cycles, then the wait time isincreased, for example the wait time doubles. If it cycles another 50times around the operating point in a relatively stable fashion, thewait time doubles again (4× the original value). As long as the systemis stable, the wait time increases, reducing the cycle frequency. If thesystem detects a different pattern, then step 910 sets ΔV and the waittime back to the starting default value.

The discussion with respect to FIG. 9 has provided an example where thewait time WAIT is increased; however, this is not a limitation of thepresent invention, and in other embodiments the wait time WAIT may bedecreased or decreased and increased at different times by any amount.The discussion with respect to FIG. 9 has provided an example where theadaptive parameter WAIT is dynamically changed during process 900;however, this is not a limitation of the present invention, and in otherembodiments other adaptive parameters, for example ΔI and ΔV, may alsobe changed. The discussion with respect to FIG. 9 has provided anexample where one adaptive parameter (WAIT) is dynamically changedduring process 900; however, this is not a limitation of the presentinvention, and in other embodiments more than one adaptive parameter maybe changed dynamically, or one or more adaptive parameters may be fixedor one or more adaptive parameters may be changed based on time periods.

FIG. 10 shows an example of a lighting system 1000 incorporating anadaptive power system 200. Similar to the system shown in FIG. 2A,adaptive power system 200 includes or consists essentially of variablevoltage supply 230, controller 220, and a current sensing system 210represented in FIG. 10 as a current sense resistor. Adaptive powersystem 200 powers a light-emitting array that includes or consistsessentially of at least one string of series-connected LEEs 110, whereeach string also includes a CCE 1010. In the example shown in FIG. 10the light-emitting array includes or consists essentially of two or morestrings of series-connected LEEs 110, and the strings are electricallycoupled in parallel. In this embodiment, CCE 1010 includes or consistsof two resistors and two transistors, for example as shown in connectionwith FIG. 2C; however, this is not a limitation of the presentinvention, and in other embodiments CCE 1010 may include or consist ofone or more passive components, one or more active components, acombination of active and passive elements, an integrated circuit, orany other mechanism for controlling the current. In operation CCEs 1010act to control the current through each string at a particular designpoint, relatively independent of the voltage value applied to thestring.

As may be seen from FIG. 10, the current sensed by resistor 210 isapproximately the sum of the current through all of the strings. Whilethis value changes with the number of strings incorporated into thesystem, the signature or shape of the I-V relationship typically doesnot substantially change with the number of strings incorporated intothe system. As has been discussed herein, the signature of the I-Vrelationship, and not its absolute value, is used to drive the voltageto the relatively optimal operating point or relative optimum operatingvoltage. Thus, systems may include or incorporate one or morelight-emitting strings or one or more groups of light-emitting strings,each having somewhat different characteristics, for example the forwardvoltage of LEEs 110, and the adaptive power system 200 will adjust andcontrol the voltage to the relatively optimal operating point. Inoperation, additional light-emitting strings or groups of light-emittingstrings may be added to or removed from the system and adaptive powersystem 200 will self-adjust to the relatively optimal operating voltage.

In various embodiments of the present invention, it may be desirable tohave a large distance between the adaptive power system and the load,for example between adaptive power system 200 and load 250 depicted inFIG. 2A. As the distance between the power source and the loadincreases, there may be an increase in loss of power transferred to theload because of, e.g., losses in the transmission medium between thepower source and the load. For example, in a lighting system, thetransmission medium may be electrically conductive elements such aswires, and as the wire length increases, for a given wire gauge, theresistive losses in the wire generally increase. As shown in FIG. 18Afor an exemplary lighting system having a long distance between theadaptive power system and the load, the resistive loss in the wire willtypically result in a lower voltage V2 at the load compared to thevoltage output V1 of the power source (here the adaptive power system).As discussed herein, for illumination systems, the adaptive power systemmeasures the current drawn by the LEE load and drives the voltage to thedesired operating point based on the I-V signature of the load, whichincludes the voltage drop in the wires, thereby automatically accountingfor the voltage drop in the wire and thereby providing the optimalvoltage to the load. In various embodiments, the voltage drop in thewire may also include other parasitic voltage drops in the system, forexample in connectors at the adaptive power system and load.

The ability for various embodiments of the present invention toaccommodate losses in the transmission medium is not limited to lossesin an electrical system. For example, in a system in which a pressure,e.g., a fluid pressure, is supplied to the load, there may beconductance losses in the pressure transfer medium, for example a pipeor tube, and the adaptive system of the present invention may be used toaccommodate for the pressure losses and provide the optimal pressure tothe load.

In various embodiments of the present invention, it may be desirable tohave different groups of light-emitting strings operating at differentcurrent levels. In some embodiments, these may be grouped together onone substrate or lightsheet, while in other embodiments these may be onseparate substrates or separate lightsheets. In some embodiments, theforward voltage of LEEs 110 varies with current, for example in the casewhere a LEE 110 includes or consists essentially of a LED, in someembodiments the current is exponentially related to the applied voltage.As the current increases, so does the forward voltage. Thus, for a fixednumber of LEEs 110 in a light-emitting string, the string voltage mayincrease with increased string current. In some embodiments, differentsubstrates or lightsheets may be designed to operate at differentcurrent levels, for example to achieve different light output powerdensities (radiant flux or luminous flux), and there will be a differentrelatively optimal operating voltage for each type of sheet (currentdrive level). The ability of the adaptive power system to vary thevoltage in response to the current needs, and the fact that the desiredvalue does not need to be programmed into the adaptive power supply,means that one adaptive power supply system may be able to drive, at arelatively optimal voltage level to achieve a high efficiency, a varietyof lighting systems or lightsheets that operate at different currentlevels with no change to the adaptive power supply. In this embodiment,the current is set by current control elements 1010 on the lightsheetand the adaptive power supply provides a variable voltage that isdynamically adjusted to the relatively optimal voltage level of thatparticular lighting system or lightsheet, based only on the signature ofthe I-V relationship, without the necessity of knowing the requiredactual current or voltage values.

Table 3 lists parameters for an exemplary lighting system including orconsisting essentially of two different parts using a fixed voltagesystem. One part is a lightsheet including or consisting oflight-emitting strings including or consisting essentially of 20GaN-based LEDs having a low, nominal and high forward voltage at about 5mA of about 2.65, 2.75, and 2.85 V respectively. In other words, thereis a distribution in the forward voltage value at about 5 mA as a resultof manufacturing or operational variations (for example changes inambient temperature) and the lighting system needs to operate correctlyacross the entire distribution. This means that it is theoreticallypossible to have all LEDs in one string have the low value for forwardvoltage and in another string all the LEDs have the high value. Whilethis scenario may be relatively unlikely, without additional sorting andbinning, it is not possible to guarantee that such a situation will notoccur, and thus it is included in the design parameters. Similarly,Table 3 shows low, medium, and high forward voltages for the secondpart, including or consisting essentially of 18 GaN based LEDs having alow, nominal, and high forward voltage at about 15 mA of about 2.85,2.95, and 3.05 V respectively. Table 3 also shows the minimum voltagerequired to operate CCE 270, which is about 1.8 V at about 5 mA andabout 2.0 V at about 15 mA. The total voltage drop across the LEDs andCCE 270 is the sum of the product of the number of LEDs per string andthe forward voltage and the voltage drop across CCE 270. The row labeled“Additional tolerance” is an extra 0.5 V that is added to accommodateany other variations as a result of other manufacturing or operationalvariation. The “Minimum required voltage” is then the sum of the“Additional tolerance” and the “LEDs+CCE voltage,” that is the minimumvoltage required to operate the circuit at the design point. As may beseen by observing the minimum required voltage for the different partswith the different distributions, the minimum required voltage variesfrom about 53.8 V to about 59.3 V. In order to power this lightingsystem with a fixed voltage system, the fixed voltage value is largeenough to power the scenario requiring the highest voltage, which inthis case is the high voltage distribution of the 5 mA part. For thisexample, a fixed applied voltage of 59.5 V is chosen. As discussedherein, the voltage not dropped across the LEDs is dropped across CCE270, and this value is shown in Table 3 for the different scenarios. Asmay be seen, the voltage dropped (and dissipated by) CCE 270 ranges fromabout 2.5 V to about 8.2 V. The power dissipated in CCE 270 may becalculated as the product of the voltage drop across CCE 270 and thecurrent through CCE 270. The efficiency of CCE 270 may also becalculated, for example as the ratio of the voltage drop across the LEDsdivided by the fixed applied voltage, and this is shown for eachscenario in Table 3. As may be seen, there is a wide range inefficiencies, depending on the part and the LED forward voltagedistribution, ranging from about 86.2% to about 95.8%. The efficiency ishigher in the scenarios in which the voltage drop across CCE 270 isrelatively low.

Now consider a similar lighting system, but operated with an adaptivepower supply of the present invention, as shown in Table 4. The sameparts and distributions are used as in the example of Table 3; however,in this case the voltage applied to each lightsheet is not fixed, as inthe example in relation to Table 3, but adapts to the relatively optimalminimal voltage. In this example the relatively optimal minimal voltageis defined as the sum of 0.5 V, the voltage drop across the LEDs, andthe voltage drop required to operate CCE 270 and is shown in Table 4 asthe “Adaptive voltage.” As may be seen from Table 4, the voltage dropacross CCE 270 with an adaptive power supply is uniformly small for allscenarios, resulting in a higher efficiency and a much tighterdistribution in efficiency values for the different scenarios. In thisexample the efficiency ranges from about 95.4% to about 96.1% foradaptive voltages ranging from 53.8 V to 59.3 V. In this example theadaptive voltage supply results in an efficiency greater than about 95%for an adaptive voltage range of about 10% of the desired operatingpoint.

FIG. 11 shows an example of a lighting system 1100 including orconsisting essentially of an adaptive power supply 200 and two or morelightsheets 1110 and 1110′. Each lightsheet 1110 and 1110′ includes oneor more light-emitting strings 160 electrically coupled in parallel,each light-emitting string 160 including or consisting essentially ofone or more light-emitting elements 110 electrically coupled in serieswith at least one CCE 270, as described in the '807 application.

TABLE 3 Unit Low Nominal High Low Nominal High Current mA 5 5 5 15 15 15Forward voltage V 2.65 2.75 2.85 2.85 2.95 3.05 # LEDs per string 20 2020 18 18 18 Total LED voltage V 53.0 55.0 57.0 51.3 53.1 54.9 Minimumvoltage to operate CCE V 1.8 1.8 1.8 2.0 2.0 2.0 LEDs + CCE voltage V54.8 56.8 58.8 53.3 55.1 56.9 Additional tolerance V 0.5 0.5 0.5 0.5 0.50.5 Minimum required voltage V 55.3 57.3 59.3 53.8 55.6 57.4 Fixedapplied voltage V 59.5 59.5 59.5 59.5 59.5 59.5 Voltage across CCE forfixed V 6.5 4.5 2.5 8.2 6.4 4.6 applied voltage CCE efficiency for fixedapplied % 89.1% 92.4% 95.8% 86.2% 89.2% 92.3% voltage

TABLE 4 Unit Low Nominal High Low Nominal High Current mA 5 5 5 15 15 15Forward voltage V 2.65 2.75 2.85 2.85 2.95 3.05 # LEDs per string 20 2020 18 18 18 Total LED voltage V 53.0 55.0 57.0 51.3 53.1 54.9 Minimumvoltage to operate CCE V 1.8 1.8 1.8 2.0 2.0 2.0 LEDs + CCE voltage V54.8 56.8 58.8 53.3 55.1 56.9 Additional tolerance V 0.5 0.5 0.5 0.5 0.50.5 Adaptive voltage V 55.3 57.3 59.3 53.8 55.6 57.4 Voltage across CCEfor adaptive V 2.3 2.3 2.3 2.5 2.5 2.5 voltage CCE efficiency for fixedapplied % 95.8% 96.0% 96.1% 95.4% 95.5% 95.6% voltage

Each lightsheet 1110 includes at least two power conductors 1130, 1140that distribute power from adaptive power supply 200 to strings 160. Atleast one lightsheet 1110 is electrically coupled to adaptive powersupply 200. In the example shown in FIG. 11, power conductor 1130 iselectrically coupled to the positive terminal of adaptive voltage supply200, while power conductor 1140 is electrically coupled to the negativeterminal of adaptive voltage supply 200. However, this is not alimitation of the present invention, and in other embodiments differentelectrical configurations and different number of power conductors 1130,1140 on lightsheet 1110 may be utilized. Additional lightsheets, forexample lightsheet 1110′, may be electrically coupled to the system byelectrically coupling like power conductors, for example throughconnections 1150, 1160, where connection 1150 electrically couples powerconductors 1130 and 1130′ and connection 1160 electrically couples powerconductors 1140 and 1140′. While FIG. 11 shows two lightsheets 1110 and1110′, this is not a limitation of the present invention, and in otherembodiments more than two lightsheets may be utilized. Some embodimentsof the present invention may include multiple adaptive power supplies200, each attached to one or more lightsheets 1110.

In some embodiments, lightsheets 1110 may each include a substrate 1210over which conductive traces 1220, 1130, 1140 have been formed toprovide interconnection between LEEs 110 and CCE 270, as shown in FIG.12. In some embodiments, substrate 1210 may be flexible, while in otherembodiments substrate 1210 may be rigid or substantially rigid.Substrate 1210 may include or consist essentially of a semicrystallineor amorphous material, e.g., polyethylene naphthalate (PEN),polyethylene terephthalate (PET), polycarbonate, polyethersulfone,polyester, polyimide, polyethylene, fiberglass, FR4, metal core printedcircuit board, (MCPCB), and/or paper. Substrate 1210 may includemultiple layers, e.g., a deformable layer over a rigid layer, forexample, a semicrystalline or amorphous material, e.g., PEN, PET,polycarbonate, polyethersulfone, polyester, polyimide, polyethylene,and/or paper formed over a rigid substrate for example comprising,acrylic, aluminum, steel and the like. Depending upon the desiredapplication for which embodiments of the invention are utilized,substrate 1210 may be substantially optically transparent, translucent,or opaque. For example, substrate 1210 may exhibit a transmittance or areflectivity greater than 70% for optical wavelengths ranging betweenapproximately 400 nm and approximately 700 nm. In some embodiments,substrate 1210 may exhibit a transmittance or a reflectivity of greaterthan 70% for one or more wavelengths emitted by LEEs 110. Substrate 1210may also be substantially insulating, and may have an electricalresistivity greater than approximately 100 ohm-cm, greater thanapproximately 1×10⁶ ohm-cm, or even greater than approximately 1×10¹⁰ohm-cm. In some embodiments substrate 1210 may have a thickness in therange of about 10 μm to about 200 μm.

Conductive elements, i.e., conductive traces 1220, 1130, 1140, may beformed via conventional deposition, photolithography, and etchingprocesses, plating processes, lamination, lamination and patterning,evaporation sputtering or the like, or they may be formed using avariety of different printing processes. For example, conductive traces1220, 1130, 1140 may be formed via screen printing, flexographicprinting, ink-jet printing, and/or gravure printing. Conductive traces1220, 1130, 1140 may include or consist essentially of a conductivematerial (e.g., an ink or a metal, metal film or other conductivematerials or the like), which may include one or more elements such assilver, gold, aluminum, chromium, copper, and/or carbon. Conductivetraces 1220, 1130, 1140 may have a thickness in the range of about 50 nmto about 1000 μm, or more preferably in the range of about 3 μm to about50 μm. In some embodiments, the thickness of conductive traces 1220,1130, 1140 may be determined by the current to be carried thereby. Whilethe thickness of one or more of conductive traces 1220, 1130, 1140 mayvary, the thickness is generally substantially uniform along the lengthof the trace to simplify processing. However, this is not a limitationof the present invention, and in other embodiments the thickness and/ormaterial of conductive traces 1220, 1130, 1140 may vary. In someembodiments, all or portions of conductive traces 1220, 1130, 1140 maybe covered or encapsulated. In some embodiments, a layer of material,for example insulating material, may be formed over all or portions ofconductive traces 1220, 1130, 1140. Such a material may include, e.g., asheet of material such as used for substrate 1210, a printed layer, forexample using screen, ink jet, stencil or other printing means, alaminated layer, or the like. Such a printed layer may include, forexample, an ink, a plastic and oxide, or the like. The covering materialand/or the technique by which it is applied is not a limitation of thepresent invention.

In one embodiment, the conductive traces 1220 are formed with a gapbetween adjacent conductive traces, and LEEs 110 and CCEs 270 areelectrically coupled to conductive traces 1220 using conductiveadhesive, e.g., an isotropically conductive adhesive and/or ananisotropic conductive adhesive (ACA). FIG. 13 shows one example of anLEE 110 electrically coupled to conductive traces 1210 using an ACA1310. ACAs may be utilized with or without stud bumps and embodiments ofthe present invention are not limited by the particular mode ofoperation of the ACA. For example, the ACA may be pressure-activated orutilize a magnetic field rather than pressure (e.g., the ZTACH ACAavailable from SunRay Scientific of Mt. Laurel, N.J., for which amagnetic field is applied during curing in order to align magneticconductive particles to form electrically conductive “columns” in thedesired conduction direction). Furthermore, various embodiments utilizeone or more other electrically conductive adhesives, e.g., isotropicallyconductive adhesives, non-conductive adhesives, in addition to orinstead of one or more ACAs. In other embodiments, LEEs 110 and CCEs 270may be attached to and/or electrically coupled to conductive traces 1220by other means, for example solder, reflow solder, wave solder, wirebonding, or the like. The technique by which LEEs 110 and CCEs 270 areattached to conductive traces 1220 is not a limitation of the presentinvention.

In some embodiments, each LEE 110 includes or consists essentially of abare semiconductor die (e.g., a bare-die LEE is an unpackagedsemiconductor die), while in other embodiments LEE 110 includes orconsist essentially of a packaged LED. In some embodiments, LEE 110includes or consists essentially of a packaged surface-mount-device-typeLED. In some embodiments, an LEE may include or consist essentially of aLED and a light-conversion material such as a phosphor. In someembodiments, an LEE may include or consist essentially of a LED and alight-conversion material, the combination of which producesubstantially white light. In some embodiments, the white light may havea correlated color temperature (CCT) in the range of about 2000 K toabout 10,000 K.

In some embodiments, LEE 110 may include or consist essentially of anLED. In some embodiments, LEE 110 may emit electromagnetic radiationwithin a wavelength regime of interest, for example, infrared, visible,for example blue, red, green, yellow, etc. light or radiation in the UVregime, when activated by passing a current through the device. In someembodiments, LEE 110 may include or consist essentially of a substrateover which the active device layers are formed. The structure andcomposition of such layers are well known to those skilled in the art.In general, such a layer structure (e.g., for an LED) may include topand bottom cladding layers, one doped n-type and one doped p-type, andone or more active layers (from which most or all of the light isemitted) in between the cladding layers. In some embodiments, the layerscollectively may have a thickness in the range of about 0.25 μm to about10 μm. In some embodiments, the substrate is transparent and all or aportion thereof is left attached to the device layers, while in otherembodiments the substrate may be partially or completely removed. Insome embodiments LEE 110 may include or consist essentially of anitride-based semiconductors (for example containing one more of theelements Al, Ga, In, and nitrogen). In some embodiments, LEE 110 mayinclude or consist essentially of a nitride-based semiconductors (forexample containing one more of the elements Al, Ga, In, and nitrogen)and may emit light in the wavelength range of about 400 nm to about 500nm.

In some embodiments, LEE 110 may be at least partially covered bywavelength-conversion material (also referred to herein as a phosphor),PCE, WCE or phosphor element (PE), all of which are utilizedsynonymously herein unless otherwise indicated. In some embodiments,white light may also be produced by combining the short-wavelengthradiant flux (e.g., blue light) emitted by the semiconductor LED withlong-wavelength radiant flux (e.g., yellow light) emitted by, forexample one or more phosphors within the light-conversion material. Thechromaticity (or color), color temperature, and color-rendering indexare determined by the relative intensities of the component colors. Forexample, the light color may be adjusted from “warm white” with acorrelated color temperature (CCT) of 2700 Kelvin or lower to “coolwhite” with a CCT of 10,000 Kelvin or greater by varying the type oramount of phosphor material. White light may also be generated solely orsubstantially only by the light emitted by the one or more phosphorparticles within the light-conversion material. In some embodiments, thestructure including or consisting essentially of LEE 110 and alight-conversion material may be referred to as a “white die.” In someembodiments, white dies may be formed by forming a light-conversionmaterial over and/or around one or more LEEs 110 and then separatingthis structure into individual white dies as described in the '864application. However, this is not a limitation of the present invention,and in other embodiments a light-conversion material may be integratedwith an LEE using a variety of different techniques.

While the discussion to this point has been in reference tolight-emitting systems, this is not a limitation of the presentinvention and in other embodiments the adaptive power supply may beutilized with any system including or consisting essentially of an I-Vcurve having a signature on which a relatively optimal operating pointmay be identified. For example adaptive power supplies may be used inconjunction with a variety of systems and loads, including but notlimited to computers, printers, displays, televisions, audio equipment,scanners, radios, commercial electronics, and the like.

While the discussion to this point has been in reference to AC poweredsystems, for example the power supply topology shown in FIG. 6A, this isnot a limitation of the present invention, and in other embodiments theadaptive power supply may be DC powered, for example by a battery orother DC power source. For example adaptive power supplies using DC orbattery power may be used in conjunction with a variety of systems andloads, including but not limited to computers, printers, displays,televisions, audio equipment, scanners, radios, mobile phones, laptopcomputers, tablets, walkie-talkies, flashlights, portable radios,personal music devices, personal video devices, portable commercial andpersonal electronics, and the like.

In various embodiments of the present invention, it may be desirable todim or reduce the intensity of light from an illumination systemutilizing an adaptive power system. In various embodiments of thepresent invention, dimming may be accomplished by modulation of thevoltage applied to the lighting system, for example modulation of theapplied voltage as described in reference to FIGS. 3A and 3B. FIG. 14Ashows a schematic of an adaptive power system incorporating a switch1410 and a switch controller 1420. In some embodiments of the invention,switch 1410 may be configured to interrupt current flow from voltagesource 130 to load 250. By varying the amount of time that switch 1410is open relative to the amount of time that it is closed, the amount ofpower applied to load 250 (and, in a lighting system, the intensity oflight thereby emitted by an LEE load 250) may be varied and controlled.In some embodiments, the control of the switch takes the form of pulsewidth modulation, in which the duty cycle of a fixed or substantiallyfixed periodic signal is applied to switch controller 1420, causingswitch 1410 to be closed during a portion of the period of the periodicsignal and to be open for the remainder of the period of the periodicsignal.

FIG. 14B shows a schematic of one example of pulse width modulation, inwhich the x-axis represents time and the y-axis represents voltage. Thetime period P1 is the period of the repeating or modulation signal, witha frequency given by 1/(P1). When the duty cycle of the modulationsignal, identified as P2 in FIG. 14B, is less than P1, the power to theload is reduced, and for an illumination system, the light output isrelatively reduced. When the duty cycle is relatively longer, forexample P2′, the output may be at a medium level, and for anillumination system, the light output is relatively increased comparedto a duty cycle of P2. When the duty cycle P2 equals or substantiallyequals the period P1 the system is fully on, and when the duty cycle iszero or substantially zero the system is off, i.e., there is no output(for example, in an illumination system, there is no light emitted bythe lighting system).

FIG. 14C shows an expanded version of FIG. 14B. As may be seen, theapplied voltage V is modulated between essentially zero and the value V.Referring to FIG. 14C, it is clear that if this type of modulation wereapplied to an adaptive system such as that shown in FIG. 2A, and if thestep of measuring the current after a voltage change, for example step415 or step 425 of process 400 shown in FIG. 4, were performed at timet3, or at any time during time period 1430, the current would not berepresentative of the actual relationship between the applied voltageand the current and might in fact be zero or substantially zero. On theother hand, if the current were measured at t4, or at any time duringtime period 1440, the measured current would in general berepresentative of the actual relationship between the applied voltageand the current.

In some embodiments of the present invention, the modulated signal, suchas that shown in FIG. 14D, may not be a perfect square wave, but in factmay have a rise time 1450 and a fall time 1455. In such embodiments, thecurrent may be measured during period 1448 to achieve a current valuerepresentative of the actual current-voltage relationship of the load.

In the examples discussed in reference to FIGS. 14C and 14D, it isassumed that the response to a voltage or input change, for example thecurrent, responds immediately or substantially immediately and has awaveform the same as or substantially the same as the voltage or inputsignal; however, this is not a limitation of the present invention, andin other embodiments, there may be a time lag between the input changeand the output response (e.g., a time lag between the voltage change andthe resulting current response), and/or there may be a difference in theshape of the output (e.g., current) waveform and the input (e.g.,voltage) waveform. For example, FIG. 15A shows an example in which theoutput (current) waveform 1520 has a relatively large rise time and falltime compared to input (voltage) waveform 1510. FIG. 15B shows anexample in which the output (current) waveform 1520 has a delay andrelatively large rise time and turns off earlier than input (voltage)waveform 1510. In such embodiments, additional constraints and/orsynchronization may be utilized to ensure that the output (current) ismeasured at a time that provides a value representative of the actualinput-output (e.g., current-voltage) relationship of the load.

While FIG. 14C shows a square wave or a substantially square wavemodulation and FIG. 14D shows a square wave with a rise and fall time,these are not limitations of the present invention, and in otherembodiments the modulation signal may have other forms, for example asawtooth waveform, a triangle waveform, a sinusoidal waveform, or thelike. The specific shape of the input and/or output (e.g., voltageand/or current) waveform is not a limitation of the present invention.

FIG. 16A depicts an exemplary adaptive power system 1600 in accordancewith embodiments of the present invention, although alternative systemswith similar functionality are also within the scope of the invention.As depicted, adaptive power system 1600 includes or consists essentiallyof variable voltage source 230, sense element 210, controller 220, amodulation controller 1620, and a switch 1610. Adaptive power system1600 is connected to a load 250 (e.g., one or more LEEs orlight-emitting strings). As described herein, controller 220 directsvariable voltage source 230 to supply a specific voltage in response toa process embedded within controller 220 and the value of the currentsensed by sense element 210. In parallel, modulation controller 1620directs switch 1610 to open and close in response to a modulation signal1621. Additionally, controller 220 and modulation controller 1620communicate together and/or are synchronized such that the current isonly sensed by sense element 210 when appropriate (as detailed above).

FIG. 16B shows an example of a current-voltage relationship of anadaptive power system of the current invention. In time period 1640, nomodulation is being applied to the system (i.e., switch 1610 is closedand is not being opened) and the voltage applied to the system, asdetermined by the adaptive controller, is voltage V1. In time period1641, modulation controller 1620 is modulating switch 1610, as shown bywaveforms 1510 (voltage) and 1520 (current). In time period 1641, thecurrent may be measured during time period 1630. In time period 1642,the adaptive controller has changed the output voltage to voltage V2,and the current may be measured during time period 1635. In someembodiments of the present invention, the rate at which the adaptivecontroller modifies the voltage from variable voltage source 230 may beless than the rate at which modulation controller 1620 modulates switch1610, while in other embodiments of the present invention the rate atwhich the adaptive controller modifies the voltage from variable voltagesource 230 may be greater than the rate at which modulation controller1620 modulates switch 1610.

In various embodiments of the present invention, the time period 1630(and the time periods associated with currents 1651 and 1652 which arenot labelled in FIG. 16B) during which a current measurement may beperformed may be optimized for different operational characteristics ofthe adaptive system. For example, if it is desired for the system todetermine the optimal voltage with high accuracy, then a high-resolutioncurrent measurement may be performed. In various embodiments, thismeasurement takes time, and the time may increase with the desiredresolution and potentially with the range of currents that may bepresent. In order to make an accurate measurement, the measurement timeis typically less than time period 1650. In various embodiments of thepresent invention, this constraint may set a minimum dimming level,because the dimming level set by the duty cycle of modulation controller1620 and the period of the PWM frequency will need to be at least aslarge as the measurement time. If the PWM period is given by t, and themeasurement time is m, then the minimum dimming level is approximatelygiven by m/t. For example for a PWM frequency of about 2 kHz, whichcorresponds to a period of about 500 μs, and a measurement time of about50 μs, the minimum dimming level is about 10% (i.e., of the full-scaleof illumination levels outputtable by the load). Dimming levels belowthis minimum dimming (or “threshold”) level may cause inaccurate currentmeasurements; thus, in various embodiments of the present invention, thecontrol system may not perform the adaptive functions (for examplemeasure the current or adjust the voltage) and may hold the last voltagesetting constant when the dimming level is below the threshold value.

In various embodiments of the present invention, LEEs 110 may include orconsist essentially of light-emitting diodes (LEDs). In variousembodiments, the forward voltage of the LEDs may shift with LEDtemperature (for example, the LED junction temperature), and thedirection and extent of the shift is dependent on the structure andmaterials of the LED. Many LEDs exhibit an increase in forward voltagewith decreasing LED temperature, and thus at low dimming levels,particularly for extended periods of time, the LED temperature maydecrease, resulting in an increase in LED voltage. If the adaptivefunction is temporarily suspended at low dimming levels, then the loadvoltage requirement may increase over time at the low dimming level, andthis increased requirement may not be supplied by the power supplybecause the adaptive function is temporarily disabled while the dimminglevel is below the threshold.

In various embodiments, this effect may be mitigated by the use of anopen-loop control system that temporarily replaces the adaptive functionwhen the dimming level is below the threshold value. For example, if thedimming level is below the threshold value and the adaptivefunctionality is temporarily disabled, the system may increase theoutput voltage based on the amount of time the dimming level has beenbelow the threshold. For example, the system may start a timer when thedimming level drops below the threshold value and, based on the timeelapsed, increase the output voltage, for example based upon analgorithm or a look-up table. The relationship between the dimming leveland the junction temperature may be determined experimentally and usedto produce the relationship between time and voltage for differentdimming levels, e.g., 10%, 5%, and 1%, or other dimming levels inbetween. Table 5 is an example of a look-up table that may be used foradjusting the output voltage when the dimming level is set below thethreshold value for an elapsed time t. As indicated, the voltageadjustment is a relative increase in the output voltage applied to theload regardless of what the absolute voltage level was prior to dimmingbelow the threshold level. In this example, T1<T2<T3<T4 andV1<V2<V3<V4<V5. In various embodiments, this information may be coded orembodied in a look-up table, an equation, an algorithm, or the like. Theform of the relationship between t and V may be linear or exponential ormay have any form.

TABLE 5 Elapsed Time Voltage Increase t < T1 V1 T1 < t < T2 V2 T2 < t <T3 V3 T3 < t < T4 V4 t > T4 V5

For example, in various embodiments T1 may be in the range of about 2seconds to about 20 seconds, T2 may be in the range of about 10 secondsto about 40 seconds, T3 may be in the range of about 20 seconds to about2 minutes, and T4 may be in the range of about 1 minute to about 10minutes. In an exemplary embodiment, T1 may be about 10 seconds, T2 maybe about 30 seconds, T3 may be about 1 minute, and T4 may be about 5minutes, and V1 may be about zero, V2 may be about 100 mV, V3 may beabout 250 mV, V4 may be about 500 mV, and V5 may be about 1V. In otherembodiments, the elapsed time thresholds and voltage increase steps maybe different, and there may be more or fewer time and voltage steps, asthis is not a limitation of the present invention.

In various embodiments of the present invention, a temperature sensorattached to the LEE load may be read in order to determine the actualLEE temperature as a function of time, which the system may use todetermine a more accurate output voltage adjustment to match the LEEload based on a known relationship of the voltage to LEE junctiontemperature. This voltage adjustment may again be defined in a look-uptable, an equation, an algorithm, or be calculated in real time by thesystem.

In various embodiments which don't require optimal voltage control forboth large and small loads and thus don't need as high an accuracy forcurrent measurement, it may be possible to perform A/D conversions in ashorter time. For example, in various embodiments, relatively lowercurrent measurements may be performed in a time range of about 1 us toabout 25 μs. If the PWM frequency is in the range of about 2 kHz (whichtranslates to a period of 500 μs) and the current measurement time is 5μs, then the minimum dimming duty cycle which may be accommodated andstill allow a current measurement to be made accurately is approximately1%.

In various embodiments which may require optimal voltage control forboth large and small loads, as well as accurate current measurement evenfor low dimming levels, a lower PWM frequency may be used. For example,if the PWM frequency is in the range of 200 Hz (which translates to aperiod of about 5 ms), and the high accuracy A/D conversion takes, forexample, up to 50 us to perform, then the minimum dimming duty cyclewhich may be accommodated and still allow a current measurement to bemade accurately is approximately 1%.

In various embodiments of the present invention, the value of the output(current) may be averaged over more than one modulation cycle, forexample to achieve a more representative value of the output (current)or to reduce the noise or variation in the value of the output. Forexample, the value of currents 1650, 1651, and 1652 may be averagedbefore being processed by controller 220. In some embodiments, theaveraging may be performed in controller 220, while in other embodimentsthe averaging may take place in a different part or component of thesystem.

In some embodiments of the present invention, the modulation frequency,for example the frequency at which switch 1610 is modulated, may be inthe range of about 100 Hz to about 5000 Hz. In some embodiments, thefrequency with which the adaptive power system samples the voltage andmeasures the current may be less than 100 Hz, for example in the rangeof about 10⁻⁶ Hz to about 100 Hz. In some embodiments of the presentinvention, the modulation frequency is in the range of about 500 Hz toabout 2000 Hz, and the frequency with which the adaptive power systemsamples the voltage and measures the current is in the range of about10⁻⁴ Hz to about 10 Hz. In some embodiments, the output signal may beaveraged over 10 modulation periods, over 100 modulation periods, over1000 modulation periods or over more modulation periods.

In some embodiments of the present invention, modulation controller 1610and controller 220 may be separate functionally or physically, while inother embodiments modulation controller 1610 and controller 220 may beone unit, physically and/or functionally. In some embodiments of thepresent invention, switch 1610 may include or consist essentially of amechanical switch, for example a relay, or may be a semiconductor switch(e.g., one or more transistors) or may be any other type of system; themethod of modulating the input signal is not a limitation of the presentinvention. For example, in some embodiments of the present invention,the output signal may be in the form of a light wave and switch 1610 maybe in the form of a mechanical chopper or electro-optic modulation cell.

Modulation signal 1621 may take many forms. In some embodiments, it isan electrical signal and may conform to a number of differentcommunication or signal protocols. For example, modulation signal 1621may be a 0-10V signal, a 4-20 mA signal, a DALI signal, a DMX signal, orthe like. The specific type and configuration of modulation signal 1621is not a limitation of the present invention. In some embodiments of thepresent invention, modulation signal 1621 may originate in a manuallycontrolled unit, for example a wall switch or dimming unit, a sensor,for example a daylight or occupancy sensor, a building managementsystem, a portable device like a cellular phone or tablet, or the like.The origin of modulation signal 1621 is not a limitation of the presentinvention.

In some embodiments of the present invention, modulation of the input tothe system, for example the voltage, may be accommodated by the adaptivepower system by integrating the output signal over a period of time andscaling it by the duty cycle of the input signal and the time period.FIG. 17 shows one example of a voltage input and a current output. Let

P_(n)=# of periods of modulation over which the integration isoccurring;

T_(d)=duty cycle of modulation=period 1710/period 1720;

I=value of current when input voltage is applied to load; and

I_(t)=value of current integrated over P_(n) periods (units of A-sec).

Integrating the current over P_(n) periods gives a value of I_(t) A-sec.I_(t)=I×P_(n)×T_(d). In this example, I may be determined by dividingI_(t) by (P_(n)×T_(d)). For example, in one embodiment of the presentinvention, I is about 1 A, T_(d) is about 50%, and P_(n) is 100. Thevalue of I_(t) is then 50 A-sec. Dividing this by (P_(n)×T_(d)), or 50,then provides the actual value of I. In this embodiment of the presentinvention, the current has a square waveform or substantially squarewaveform; however, this is not a limitation of the present invention,and in other embodiments the current and/or voltage (output and/orinput) may have other waveform shapes, as described herein.

While FIG. 17 shows T_(d) as constant or substantially constant over thetime period P_(n) this is not a limitation of the present invention, andin other embodiments T_(d) may vary within P_(n) in which case I_(t) maybe determined, for example, as a sum of current elements from eachperiod:

${It} = {{\sum\limits_{Pn}\;{I \times T_{d}}} = {\sum( {{I \times T_{d\; 1}} + {I \times T_{d\; 2}} + {I \times T_{d\; 3}} + \ldots}\mspace{11mu} )}}$

I may then be calculated from I_(t) by the equation:

$I = \frac{I_{t}}{P_{n} \times \Sigma\; T_{d}}$

The equation for calculation of the current value may in someembodiments depend on the specific waveform shape. In some embodimentsof the present invention, the waveform shape may be pre-determined andused to formulate an equation to determine the output value to asufficient level of accuracy. In other embodiments of the presentinvention, the shape of the current waveform may be determined by theadaptive power system, for example by controller 220, and the determinedwaveform may be used to formulate an equation to determine the outputvalue to a sufficient level of accuracy. In some embodiments of thepresent invention, the waveform shape may be determined once or atperiodic intervals, while in other embodiments the waveform shape may bedetermined in real time during each period of modulation.

In various embodiments of the present invention, integration of thecurrent waveform may be accomplished by a digital-to-analog (DAC)conversion process. In various embodiments of the present invention, theDAC process may be performed by a microprocessor or microcontroller orother digital system; however, this is not a limitation of the presentinvention, and in other embodiments the DAC process may be performed inthe analog domain, for example by using a low-pass filter.

In various embodiments of the present invention, it may be desirable topower one or more adaptive systems from one primary power source. Forexample, FIG. 18 shows a primary power source 1810 providing power totwo adaptive systems 1820 and 1830, which are connected to loads 1825and 1835 respectively; however, this is not a limitation of the presentinvention, and in other embodiments one or more than two adaptivesystems may be utilized and each adaptive system may have more than oneload connected thereto. In various embodiments, it may be desirable tohave a long distance between primary power source 1810 and adaptivesystems 1820 and 1830. As discussed herein, a voltage 1842 at theadaptive systems may be less than a voltage 1840 at the output of theprimary power source 1810. In various embodiments, the voltage drop maybe too large to be accommodated by the adaptive power systems to providethe desired or optimal voltage to the load. In various embodiments ofthe present invention, one or more of the adaptive systems mayincorporate a boost circuit that is configured to boost the voltage 1842to a higher desired value. An example of a suitable boost circuit hasbeen described in U.S. patent application Ser. No. 14/664,025, filed onMar. 20, 2015, the entire disclosure of which is incorporated herein byreference. In various embodiments, the voltage 1842 is lower thanrequired, and it is boosted in adaptive systems 1820 and 1830 to ahigher value that is required by loads 1825 and 1835; the system willoperate as intended, and the adaptive power system may then set anoptimal voltage for loads 1825 and 1835, regardless of the voltage dropbetween voltages 1840 and 1842. As described with respect to FIG. 18 andherein, various embodiments of the present invention may be configuredto accommodate voltage loss along long conductor runs for a variety ofsystem and circuit configurations.

In various embodiments of the present invention, the adaptive system maybe utilized to accommodate a change in the number of LEDs in a system,for example as described in U.S. Provisional Patent Application No.62/175,725, filed Jun. 15, 2015 (the '725 application), the entiredisclosure of which is incorporated by reference herein. For example,consider a system featuring one or more strings of series-connected LEEsas shown in FIG. 19A. FIG. 19A depicts an exemplary lighting apparatus1900 in accordance with various embodiments of the present invention.Lighting apparatus 1900 includes a substrate 1965 on which are disposedconductive elements 1924, power conductors 1920, 1921, control elements1945, LEEs 110, and bypass elements 1910. The circuit on substrate 1965is powered by a power supply 1970. Lighting apparatus 1900 includesthree strings 1940, 1941, and 1942 of series-connected LEEs 110;however, this is not a limitation of the present invention, and in otherembodiments lighting apparatus 1900 may include fewer or more strings.In FIG. 19A each string includes six LEEs 110; however, this is not alimitation of the present invention, and in other embodiments lightingapparatus 1900 (and/or each string thereof) may include fewer or moreLEEs 110. In various embodiments of the present invention, each LEE 110may represent one LEE or may represent a group of two or more LEEs, aswill be discussed herein.

Substrate 1965 may be shortened in the direction 1950 by removing firststring 1940 (for example by cutting along cut line A-A′) and then string1941 (for example by cutting along cut line B-B′). In variousembodiments of the present invention, the size increment removed wheneach string removed is equal to or substantially equal to a pitch (orspacing) 1923. In various embodiments, pitch 1923 may be in the range ofabout 3 mm to about 200 mm. In various embodiments, pitch 1923 may be inthe range of about 5 mm to about 50 mm. This structure permitsrelatively fine control of the size increment when configuring sheet1965, as described in, for example, the '027 application, the '807application, and the '725 application.

Reduction of the size of substrate (or “sheet”) 1965 in theperpendicular or substantially perpendicular direction 1952 may beaccomplished by removing a first LEE group 1931 (for example by cuttingalong cut line C-C′), then by removing an LEE group 1932 (for example bycutting along cut line D-D′), then removing an LEE group 1933 (forexample by cutting along cut line E-E′). When the first LEE group 1931is removed, it leaves an open circuit that is shunted by one or more ofthe bypass elements 1910. In various embodiments, bypass element 1910 isor provides an open circuit or a substantially high resistance tocurrent flow when the LEEs of group 1931 are present, and is or providesa short circuit or substantially low resistance to current flow whenLEEs of group 1931 are removed.

In various embodiments of the present invention, one or more of thebypass elements 1910 may include or consist essentially of a switch, forexample a manually operated switch such as a DIP switch that may, insome embodiments, be mounted on substrate 1965. When a group of LEEs isremoved, the associated switch is closed, completing the circuit. Forexample, if LEE 110′ is removed, then switch or bypass element 1910′ isclosed to complete the circuit.

In various embodiments of the present invention, bypass element 1910 maybe activated by the action of cutting or shortening of the sheet. FIG.19B shows an example of such an embodiment, in which bypass element 1910includes or consists essentially of a normally closed relay (only aportion of the circuit is shown for clarity). Relay 1910 includes orconsists essentially of a switch 1916 and a coil 1914. Before cuttingalong cut line C-C′ to remove LEE 110′, coil 1914 is energized bycurrent flowing from a wire 1981 (herein, references to “wires” areunderstood to encompass conductive traces or other electricalconductors, and are not limited to discrete wires bonded to differentpoints on a substrate) to the coil and returning to a wire 1980, thusholding switch 1916 open, ensuring normal circuit operation. However,when LEE 110′ is removed by cutting along cut line C-C′, this also cutswires 1981, 1980, which de-energizes coil 1914, permitting switch 1916to close, thus completing the circuit. As will be understood by thoseskilled in the art, the function performed by relay 1910 may beaccomplished by means other than a conventional relay, for example asolid-state relay or other solid-state components acting as a switch orsubstantially like a switch, for example transistors such as bipolartransistors, field-effect transistors, diodes, or the like.

FIG. 19C shows an example of an embodiment of the present invention inwhich bypass element 1910 includes or consists essentially of atransistor-based circuit. In this example, bypass element 1910 includesa transistor 1918 and a resistor 1917. Before cutting along cut lineC-C′ to remove LEE 110′, the base of transistor 1918 is tied to groundby a wire 1983, the base emitter voltage V_(BE) of transistor 1918 isessentially zero, resulting in no current flow from the collector to theemitter (in essence an open circuit), thus ensuring normal circuitoperation. However, when LEE 110′ is removed by cutting along cut lineC-C′, this also cuts wire 1983, which removes the short across the baseand emitter of transistor 1918. V_(BE) increases by virtue of currentflowing through resistor 1917, turning on transistor 1918, which nowacts like a closed switch, completing the circuit.

In various embodiments of this approach, removing one or more LEEs 110may result in a reduction in the string voltage, i.e., the voltage ofthe series-connected string of LEEs 110. Referring back to FIG. 2B, FIG.2B shows a schematic of one string 160 of an exemplary lighting systemincluding current control element 270 and 20 LEEs. The string voltage isgiven by the sum of the voltage drop across current control element 270and the voltage drop across the 20 LEEs, for example V_(CCE)+n×V_(LEE),where V_(CCE) is the voltage drop across current control element 270, nis the number of LEEs in series (in FIG. 2B, n=20), and V_(LEE) is thevoltage drop across each LEE. In various embodiments, each LEE mayinclude or consist essentially of a light-emitting diode (LED), andV_(LEE) then represents the forward voltage V_(f) of the LED at theoperating current. For the present discussion it is assumed that eachLEE or LED has the same V_(LEE) or V_(f) respectively; however, invarious embodiments V_(LEE) or V_(f) may have a range of values, forexample because of manufacturing variations, component aging,temperature variations across the components, or the like.

When one or more LEEs are removed from the circuit, the string voltagetypically decreases. For a constant voltage system, in which, e.g., aconstant voltage is supplied by power supply 1970 in FIG. 19A, thestring voltage may be required to match or substantially match thevoltage supplied by power supply 1970. In various embodiments of thepresent invention, current control element 1945 may take up oraccommodate some voltage difference between the sum of the LEE forwardvoltages and the power supply voltage. However, in various embodiments,current control element 1945 may not be able to take up or accommodate arelatively larger voltage increment that may be present by removal ofone or more LEEs from the string. In various embodiments, power supply1970 may include or consist essentially of an adaptive power supply thatadjusts, i.e., reduces, its output value in response to removal of oneor more LEEs from the string. In various embodiments, the shape of theI-V relationship of the string of LEEs is the same or similar,independent of the number of LEEs in the string. For example, considerthe I-V curves shown in FIG. 3B, and assume that curve 308 is the“nominal” curve for a system with a fully populated string. When one ormore LEEs is removed from the string, for example by cutting along C-C′in FIG. 19A, the I-V curve shifts to the left (to lower voltage), forexample to curve 302. On curve 308, the “nominal” operating point ispoint 370. After removal of one or more LEEs, the operating point shiftsapproximately to point 340 on curve 302 (the voltage drops, but thecurrent stays substantially the same). At this point, the adaptiveprocess drives the output voltage to the operating point of curve 302,as described herein, resulting in a reduction in the output voltage ofthe adaptive power supply to match the voltage requirement of the systemwith fewer LEEs. This process is similar or the same as that describedherein, except that in various embodiments the change in voltagerequired to accommodate removal of one or more LEEs may be larger thanthe change in voltage required to accommodate voltage changes brought onby component value shift from aging or environmental changes.

In various embodiments of the present invention, an adaptive system mayoperate to control the voltage applied to the load to achieve an optimalset point to accommodate for the voltage drop anticipated on long cableruns or other components in the system between the power source and theload. FIG. 20 shows an example of one such embodiment. A power source2000 supplies power to a load 2100 via a switching element 2200.Switching element 2200 may be modulated as discussed herein to providedimming control for the load via a modulation signal 2310 generated bycontroller 2300. Controller 2300 may also sense the output voltage ofpower source 2000 via a sense signal 2330 and feedback a control signal2320 to regulate the output voltage. A sensing element 2400 mayindependently monitor the output voltage via a sense signal 2410 andgenerate an override signal 2430 that may act to disconnect power to theload 2100 by opening switching element 2200. This may be used as asafety measure to ensure that the output voltage of power source 2000may not exceed a predetermined maximum value Vmax. In variousembodiments, sensing element 2400 may be configured with a predeterminedtrip point Vtrip having a value lower than the value of Vmax, to ensurethat Vmax is not exceeded. In various embodiments, Vtrip may bedetermined as a percentage of Vmax, for example 95% of Vmax or 98% orVmax, or the difference between Vmax and Vtrip (i.e., Vmax−Vtrip) may beset to a fixed value, e.g., 1 volt or 0.5 volt. The percentage orabsolute value difference between Vmax and Vtrip is not a limitation ofthe present invention. Additionally, in various embodiments, sensingelement 2400 may generate an overvoltage trip signal 2420 to alert thecontroller that the output voltage has exceeded Vmax.

In various embodiments of the present invention, controller 2300 may beconfigured so it cannot set the output voltage above the Vtrip point,but instead may set it to some optimal voltage based on the V-Icharacteristic of the load 2100 as discussed herein, in which case undernormal operating conditions the output voltage will always remain belowVtrip and sensing element 2400 will never send the override signal 2430.In various other embodiments, controller 2300 may be configured to beable to set the output voltage up to or higher than Vtrip in order to beable to maximize the possible run length for a given system. In thiscase, one possible control algorithm to find the trip point and set thisoptimal voltage is:

-   -   1. Controller 2300 turns off switching element 2200 and sets        output voltage Vout of power source 2000 to Vh, which is the        maximum setting available (Vh=Vtrip+/−delta).    -   2. If overvoltage trip signal is not present, then Vout<Vtrip,        then delta is negative so Vout may be applied to the load, or a        predetermined lower voltage may be set, for example Vout−0.5V.    -   3. If overvoltage trip signal is present, then Vout>Vtrip, so        reduce Vout by a predetermined step, for example 0.1V.    -   4. Repeat from Step 2.

In another embodiment, the output voltage is continuously monitoredduring operation via sense signal 2330. If the measured voltage driftsabove the stored set point due to either internal malfunction orexternal factors such as temperature effects, etc., controller 2300 maystep the voltage down further by a predetermined amount, for example0.1V, to ensure the output voltage does not reach Vtrip, which mayundesirably cause the load to shut off unexpectedly.

It is to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. As used herein, the terms “substantially”and “approximately” mean±10%, and in some embodiments, ±5%. As usedherein, the term “phosphor” refers to any material that shifts thewavelength of light striking it and/or that is luminescent, fluorescent,and/or phosphorescent.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is:
 1. A method for controlling, via application offirst and second voltages, a circuit incorporating a load having anon-linear current-voltage relationship, the method comprising: (A)applying the first voltage to the load; (B) measuring a first currentresulting from the first voltage applied to the load; (C) applying thesecond voltage to the load; (D) measuring a second current resultingfrom the second voltage applied to the load, a current differencebetween the second current and the first current having a magnitude; (E)altering the second voltage by a voltage increment having a magnitudeand polarity based at least in part on the magnitude of the currentdifference between the second current and the first current; and (F)repeating steps (A)-(E) during operation of the circuit to regulateoperation of the load notwithstanding any changes in the non-linearcurrent-voltage relationship of the load during operation.
 2. The methodof claim 1, further comprising setting the first current equal to thesecond current after step (D).
 3. The method of claim 1, wherein thesecond voltage is increased above a maximum operating voltage, furthercomprising decreasing the second voltage to the maximum operatingvoltage or less prior to applying the second voltage to the load.
 4. Themethod of claim 1, wherein the voltage increment decreases as a numberof times steps (A)-(E) are repeated increases.
 5. The method of claim 1,wherein the magnitude and polarity of the voltage increment aredetermined from a table of pre-determined rules.
 6. The method of claim1, wherein the non-linear current-voltage characteristic of the loadcomprises at least one of a global minimum or a global maximumtherewithin.
 7. The method of claim 1, wherein the load comprises alighting system, an intensity of light emitted by the lighting systembeing at least partially determined by a current at which the lightingsystem operates.
 8. The method of claim 1, wherein the non-linearcurrent-voltage characteristic of the load comprises at least one of alocal minimum or a local maximum therewithin.
 9. The method of claim 1,wherein step (E) comprises: (i) if the magnitude of the currentdifference is greater than a pre-determined value, increasing the secondvoltage by the voltage increment; and (ii) if the magnitude of thecurrent difference is smaller than the pre-determined value, decreasingthe second voltage by the voltage increment.
 10. The method of claim 1,further comprising (i) receiving an output voltage from a primary powersource, and (ii) boosting the output voltage to a boosted voltage largerthan the output voltage.
 11. The method of claim 10, wherein the outputvoltage is boosted by a boost circuit discrete from and spaced apartfrom the primary power source.
 12. The method of claim 1, wherein thevoltage increment decreases during step (F) in the absence of temporaryor permanent variations of the non-linear current-voltage relationship.13. The method of claim 1, further comprising pausing for apre-determined amount of time prior to applying the second voltage tothe load.
 14. The method of claim 13, wherein the pre-determined amountof time increases as a number of times steps (A)-(E) are repeatedincreases.
 15. The method of claim 1, wherein the circuit is configuredto operate at a design point, the design point comprising a designcurrent and a design voltage.
 16. The method of claim 15, wherein thevoltage increment is less than about 10% of the design voltage.
 17. Themethod of claim 1, wherein the magnitude and polarity of the voltageincrement are determined from a comparison of a pre-determined value tothe magnitude of the current difference between the second current andthe first current.
 18. The method of claim 17, wherein thepre-determined value is constant as steps (A)-(E) repeat.
 19. The methodof claim 17, wherein (i) the circuit is configured to operate at adesign point, the design point comprising a design current and a designvoltage, and (ii) the pre-determined value is less than approximately20% of the design current.
 20. The method of claim 17, wherein thepre-determined value decreases as a number of times steps (A)-(E) arerepeated increases.
 21. The method of claim 1, wherein the loadcomprises a light-emitting array comprising: first and secondspaced-apart power conductors; and a plurality of light-emittingstrings, at least one light-emitting string (i) comprising a pluralityof interconnected light-emitting diodes spaced along the light-emittingstring, (ii) having a first end electrically coupled to the first powerconductor, (iii) having a second end electrically coupled to the secondpower conductor, wherein the power conductors supply power to each ofthe light-emitting strings.
 22. The method of claim 21, wherein thelight-emitting diodes emit substantially white light.
 23. The method ofclaim 21, wherein the light-emitting array comprises a plurality ofcontrol elements, at least one control element being (i) electricallyconnected to at least one light-emitting string and (ii) configured toutilize power supplied from the power conductors to control the currentto the at least one light-emitting string to which it is electricallyconnected.
 24. The method of claim 1, wherein, after a plurality ofrepetitions of steps (A)-(E), the circuit operates at a stable operatingrange of voltages for at least a second plurality of repetitions ofsteps (A)-(E).
 25. The method of claim 24, further comprising decreasingthe voltage increment at least once while the circuit operates at thestable operating range.
 26. The method of claim 24, further comprisingpausing for a pre-determined amount of time prior to applying the secondvoltage to the load, the pre-determined amount of time increasing atleast once while the circuit operates at the stable operating range. 27.The method of claim 26, further comprising resetting the pre-determinedamount of time to a default value if circuit operation diverges from thestable operating range.
 28. The method of claim 1, wherein thenon-linear current-voltage characteristic of the load comprises a kneetherewithin.
 29. The method of claim 28, wherein the current increasesas the voltage increases in the knee region.
 30. The method of claim 28,wherein the current decreases as the voltage increases in the kneeregion.
 31. The method of claim 1, wherein (i) a first plurality ofcycles of steps (A)-(E) repeating constitutes a start-up phase, and (ii)a second plurality of cycles of steps (A)-(E) repeating constitutes anoperation phase, the start-up phase preceding the operation phase. 32.The method of claim 31, wherein, during the start-up phase, the voltageincrement decreases as a number of times steps (A)-(E) are repeatedincreases.
 33. The method of claim 31, wherein, during the operationphase, the voltage increment decreases as a number of times steps(A)-(E) are repeated increases.
 34. The method of claim 31, wherein,after the start-up phase, the circuit operates at a stable operatingrange of voltages for at least a portion of the operating phase.
 35. Amethod for controlling, via application of first and second inputs, asystem incorporating a load having a non-linear output-inputrelationship, the method comprising: (A) applying the first input to theload; (B) measuring a first output resulting from the first inputapplied to the load; (C) applying the second input to the load; (D)measuring a second output resulting from the second input applied to theload, an output difference between the second output and the firstoutput having a magnitude; (E) altering the second input by an inputincrement having a magnitude and polarity based at least in part on themagnitude of the output difference between the second output and thefirst output; and (F) repeating steps (A)-(E) during operation of thesystem to regulate operation of the load notwithstanding any changes inthe non-linear output-input relationship of the load during operation.36. The method of claim 35, further comprising setting the first outputequal to the second output after step (D).
 37. The method of claim 35,wherein step (E) comprises: (i) if the magnitude of the outputdifference is greater than a pre-determined value, increasing the secondinput by the input increment; and (ii) if the magnitude of the outputdifference is smaller than the pre-determined, decreasing the secondinput by the input increment.
 38. The method of claim 37, wherein step(E) comprises, before altering the second input, setting the firstoutput equal to the second output.